diff --git a/fml/patches/minecraft/net/minecraft/client/Minecraft.java.patch b/fml/patches/minecraft/net/minecraft/client/Minecraft.java.patch
index ffa2859f90..80ffafed92 100644
--- a/fml/patches/minecraft/net/minecraft/client/Minecraft.java.patch
+++ b/fml/patches/minecraft/net/minecraft/client/Minecraft.java.patch
@@ -44,7 +44,7 @@
          Display.setVSyncEnabled(this.field_71474_y.field_74352_v);
      }
  
-@@ -916,9 +923,11 @@
+@@ -915,9 +922,11 @@
  
          if (!this.field_71454_w)
          {
@@ -56,7 +56,7 @@
          }
  
          GL11.glFlush();
-@@ -1496,6 +1505,8 @@
+@@ -1495,6 +1504,8 @@
              --this.field_71467_ac;
          }
  
@@ -65,7 +65,7 @@
          this.field_71424_I.func_76320_a("gui");
  
          if (!this.field_71445_n)
-@@ -1646,6 +1657,7 @@
+@@ -1645,6 +1656,7 @@
                          this.field_71462_r.func_146274_d();
                      }
                  }
@@ -73,7 +73,7 @@
              }
  
              if (this.field_71429_W > 0)
-@@ -1787,6 +1799,7 @@
+@@ -1786,6 +1798,7 @@
                              }
                          }
                      }
@@ -81,7 +81,7 @@
                  }
              }
  
-@@ -1978,6 +1991,8 @@
+@@ -1977,6 +1990,8 @@
              this.field_71453_ak.func_74428_b();
          }
  
@@ -90,3 +90,11 @@
          this.field_71424_I.func_76319_b();
          this.field_71423_H = func_71386_F();
      }
+@@ -2093,6 +2108,7 @@
+             this.field_110448_aq.func_148529_f();
+             this.func_71351_a((ServerData)null);
+             this.field_71455_al = false;
++            FMLClientHandler.instance().handleClientWorldClosing(this.field_71441_e);
+         }
+ 
+         this.field_147127_av.func_147690_c();
diff --git a/fml/src/main/java/cpw/mods/fml/client/FMLClientHandler.java b/fml/src/main/java/cpw/mods/fml/client/FMLClientHandler.java
index f2ee6384d9..d23a3bde4f 100644
--- a/fml/src/main/java/cpw/mods/fml/client/FMLClientHandler.java
+++ b/fml/src/main/java/cpw/mods/fml/client/FMLClientHandler.java
@@ -54,6 +54,7 @@ import cpw.mods.fml.common.ModContainer;
 import cpw.mods.fml.common.ModMetadata;
 import cpw.mods.fml.common.ObfuscationReflectionHelper;
 import cpw.mods.fml.common.WrongMinecraftVersionException;
+import cpw.mods.fml.common.registry.GameData;
 import cpw.mods.fml.common.toposort.ModSortingException;
 import cpw.mods.fml.relauncher.Side;
 
@@ -488,4 +489,9 @@ public class FMLClientHandler implements IFMLSidedHandler
     {
         return this.client.func_147114_u()!=null ? this.client.func_147114_u().func_147298_b() : null;
     }
+
+    public void handleClientWorldClosing(WorldClient field_71441_e)
+    {
+        GameData.revertToFrozen();
+    }
 }
diff --git a/fml/src/main/java/cpw/mods/fml/common/FMLContainer.java b/fml/src/main/java/cpw/mods/fml/common/FMLContainer.java
index d39c2f2543..29e15e5749 100644
--- a/fml/src/main/java/cpw/mods/fml/common/FMLContainer.java
+++ b/fml/src/main/java/cpw/mods/fml/common/FMLContainer.java
@@ -146,7 +146,7 @@ public class FMLContainer extends DummyModContainer implements WorldAccessContai
                 NBTTagCompound dataTag = list.func_150305_b(i);
                 dataList.put(dataTag.func_74779_i("K"), dataTag.func_74762_e("V"));
             }
-            boolean successfullyInjected = GameData.injectWorldIDMap(dataList);
+            boolean successfullyInjected = GameData.injectWorldIDMap(dataList, true);
             if (!successfullyInjected)
             {
                 throw new RuntimeException("Failed to load the world - there are fatal block and item id issues");
diff --git a/fml/src/main/java/cpw/mods/fml/common/Loader.java b/fml/src/main/java/cpw/mods/fml/common/Loader.java
index ab208de379..9878bab16a 100644
--- a/fml/src/main/java/cpw/mods/fml/common/Loader.java
+++ b/fml/src/main/java/cpw/mods/fml/common/Loader.java
@@ -496,6 +496,7 @@ public class Loader
         }
         modController.transition(LoaderState.PREINITIALIZATION, false);
         modController.distributeStateMessage(LoaderState.PREINITIALIZATION, disc.getASMTable(), canonicalConfigDir);
+        GameData.freezeData();
         modController.transition(LoaderState.INITIALIZATION, false);
     }
 
@@ -778,6 +779,7 @@ public class Loader
 
     public void serverStopped()
     {
+        GameData.revertToFrozen();
         modController.distributeStateMessage(LoaderState.SERVER_STOPPED);
         modController.transition(LoaderState.SERVER_STOPPED, true);
         modController.transition(LoaderState.AVAILABLE, true);
diff --git a/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeClientState.java b/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeClientState.java
index 9079525113..30940037ad 100644
--- a/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeClientState.java
+++ b/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeClientState.java
@@ -57,14 +57,14 @@ enum FMLHandshakeClientState implements IHandshakeState<FMLHandshakeClientState>
                 dispatcher.rejectHandshake(result);
                 return ERROR;
             }
-            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck());
+            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck(ordinal()));
             if (!ctx.channel().attr(NetworkDispatcher.IS_LOCAL).get())
             {
                 return WAITINGSERVERCOMPLETE;
             }
             else
             {
-                return COMPLETE;
+                return PENDINGCOMPLETE;
             }
         }
     },
@@ -74,13 +74,22 @@ enum FMLHandshakeClientState implements IHandshakeState<FMLHandshakeClientState>
         public FMLHandshakeClientState accept(ChannelHandlerContext ctx, FMLHandshakeMessage msg)
         {
             FMLHandshakeMessage.ModIdData modIds = (FMLHandshakeMessage.ModIdData)msg;
-            if (!GameData.injectWorldIDMap(modIds.dataList()))
+            if (!GameData.injectWorldIDMap(modIds.dataList(), false))
             {
                 NetworkDispatcher dispatcher = ctx.channel().attr(NetworkDispatcher.FML_DISPATCHER).get();
                 dispatcher.rejectHandshake("Fatally missing blocks and items");
                 return ERROR;
             }
-            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck());
+            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck(ordinal()));
+            return PENDINGCOMPLETE;
+        }
+    },
+    PENDINGCOMPLETE
+    {
+        @Override
+        public FMLHandshakeClientState accept(ChannelHandlerContext ctx, FMLHandshakeMessage msg)
+        {
+            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck(ordinal()));
             return COMPLETE;
         }
     },
@@ -89,9 +98,11 @@ enum FMLHandshakeClientState implements IHandshakeState<FMLHandshakeClientState>
         @Override
         public FMLHandshakeClientState accept(ChannelHandlerContext ctx, FMLHandshakeMessage msg)
         {
-            FMLMessage.CompleteHandshake complete = new FMLMessage.CompleteHandshake(Side.SERVER);
-            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck());
+            NetworkDispatcher dispatcher = ctx.channel().attr(NetworkDispatcher.FML_DISPATCHER).get();
+            dispatcher.completeClientHandshake();
+            FMLMessage.CompleteHandshake complete = new FMLMessage.CompleteHandshake(Side.CLIENT);
             ctx.fireChannelRead(complete);
+            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck(ordinal()));
             return DONE;
         }
     },
diff --git a/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeMessage.java b/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeMessage.java
index a9e8d475c5..75b4b7aee6 100644
--- a/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeMessage.java
+++ b/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeMessage.java
@@ -110,6 +110,12 @@ public abstract class FMLHandshakeMessage {
         {
             return modTags;
         }
+
+        @Override
+        public String toString(Class<? extends Enum<?>> side)
+        {
+            return super.toString(side)+":"+modTags.size()+" mods";
+        }
     }
 
     public static class ModIdData extends FMLHandshakeMessage {
@@ -150,9 +156,35 @@ public abstract class FMLHandshakeMessage {
         {
             return modIds;
         }
+        @Override
+        public String toString(Class<? extends Enum<?>> side)
+        {
+            return super.toString(side) + ":"+modIds.size()+" mappings";
+        }
     }
     public static class HandshakeAck extends FMLHandshakeMessage {
+        int phase;
+        public HandshakeAck() {}
+        HandshakeAck(int phase)
+        {
+            this.phase = phase;
+        }
+        @Override
+        public void fromBytes(ByteBuf buffer)
+        {
+            phase = buffer.readByte();
+        }
 
+        @Override
+        public void toBytes(ByteBuf buffer)
+        {
+            buffer.writeByte(phase);
+        }
+        @Override
+        public String toString(Class<? extends Enum<?>> side)
+        {
+            return super.toString(side) + ":{"+phase+"}";
+        }
     }
     public void fromBytes(ByteBuf buffer)
     {
@@ -162,5 +194,8 @@ public abstract class FMLHandshakeMessage {
     {
     }
 
-
+    public String toString(Class<? extends Enum<?>> side)
+    {
+        return getClass().getName().substring(getClass().getName().lastIndexOf('$'));
+    }
 }
diff --git a/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeServerState.java b/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeServerState.java
index de01c8b4ee..79315fd288 100644
--- a/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeServerState.java
+++ b/fml/src/main/java/cpw/mods/fml/common/network/handshake/FMLHandshakeServerState.java
@@ -57,7 +57,7 @@ enum FMLHandshakeServerState implements IHandshakeState<FMLHandshakeServerState>
             {
                 ctx.writeAndFlush(new FMLHandshakeMessage.ModIdData(GameData.buildItemDataList()));
             }
-            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck());
+            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck(ordinal()));
             NetworkRegistry.INSTANCE.fireNetworkHandshake(ctx.channel().attr(NetworkDispatcher.FML_DISPATCHER).get(), Side.SERVER);
             return COMPLETE;
         }
@@ -67,6 +67,8 @@ enum FMLHandshakeServerState implements IHandshakeState<FMLHandshakeServerState>
         @Override
         public FMLHandshakeServerState accept(ChannelHandlerContext ctx, FMLHandshakeMessage msg)
         {
+            // Poke the client
+            ctx.writeAndFlush(new FMLHandshakeMessage.HandshakeAck(ordinal()));
             FMLMessage.CompleteHandshake complete = new FMLMessage.CompleteHandshake(Side.SERVER);
             ctx.fireChannelRead(complete);
             return DONE;
diff --git a/fml/src/main/java/cpw/mods/fml/common/network/handshake/HandshakeMessageHandler.java b/fml/src/main/java/cpw/mods/fml/common/network/handshake/HandshakeMessageHandler.java
index c7074a79a9..008ae53512 100644
--- a/fml/src/main/java/cpw/mods/fml/common/network/handshake/HandshakeMessageHandler.java
+++ b/fml/src/main/java/cpw/mods/fml/common/network/handshake/HandshakeMessageHandler.java
@@ -1,5 +1,6 @@
 package cpw.mods.fml.common.network.handshake;
 
+import cpw.mods.fml.common.FMLLog;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.SimpleChannelInboundHandler;
 import io.netty.util.AttributeKey;
@@ -8,17 +9,20 @@ public class HandshakeMessageHandler<S extends Enum<S> & IHandshakeState<S>> ext
     private static final AttributeKey<IHandshakeState<?>> STATE = new AttributeKey<IHandshakeState<?>>("fml:handshake-state");
     private final AttributeKey<S> fmlHandshakeState;
     private S initialState;
+    private Class<S> stateType;
 
     @SuppressWarnings("unchecked")
     public HandshakeMessageHandler(Class<S> stateType)
     {
         fmlHandshakeState = (AttributeKey<S>) ((Object)STATE);
         initialState = Enum.valueOf(stateType, "START");
+        this.stateType = stateType;
     }
     @Override
     protected void channelRead0(ChannelHandlerContext ctx, FMLHandshakeMessage msg) throws Exception
     {
         S state = ctx.attr(fmlHandshakeState).get();
+        FMLLog.info(msg.toString(stateType) + "->" + state.getClass().getName().substring(state.getClass().getName().lastIndexOf('.')+1)+":"+state);
         S newState = state.accept(ctx, msg);
         ctx.attr(fmlHandshakeState).set(newState);
     }
diff --git a/fml/src/main/java/cpw/mods/fml/common/network/handshake/NetworkDispatcher.java b/fml/src/main/java/cpw/mods/fml/common/network/handshake/NetworkDispatcher.java
index 7e0b6bd5c1..0c4b7e9e36 100644
--- a/fml/src/main/java/cpw/mods/fml/common/network/handshake/NetworkDispatcher.java
+++ b/fml/src/main/java/cpw/mods/fml/common/network/handshake/NetworkDispatcher.java
@@ -36,7 +36,7 @@ import cpw.mods.fml.relauncher.Side;
 
 public class NetworkDispatcher extends SimpleChannelInboundHandler<Packet> implements ChannelOutboundHandler {
     private static enum ConnectionState {
-        OPENING, AWAITING_HANDSHAKE, HANDSHAKING, CONNECTED;
+        OPENING, AWAITING_HANDSHAKE, HANDSHAKING, HANDSHAKECOMPLETE, CONNECTED;
     }
 
     private static enum ConnectionType {
@@ -172,12 +172,7 @@ public class NetworkDispatcher extends SimpleChannelInboundHandler<Packet> imple
         {
             handled = handleClientSideCustomPacket((S3FPacketCustomPayload)msg, ctx);
         }
-        else if (msg instanceof S40PacketDisconnect && state != ConnectionState.CONNECTED)
-        {
-            // Switch to play state to handle the disconnect message
-            completeClientSideConnection();
-        }
-        else if (state != ConnectionState.CONNECTED)
+        else if (state != ConnectionState.CONNECTED && state != ConnectionState.HANDSHAKECOMPLETE)
         {
             FMLLog.info("Unexpected packet during modded negotiation - assuming vanilla or keepalives : %s", msg.getClass().getName());
         }
@@ -379,6 +374,7 @@ public class NetworkDispatcher extends SimpleChannelInboundHandler<Packet> imple
     {
         if (state == ConnectionState.CONNECTED)
         {
+            FMLLog.severe("Attempt to double complete the network connection!");
             throw new FMLNetworkException("Attempt to double complete!");
         }
         if (side == Side.CLIENT)
@@ -390,4 +386,9 @@ public class NetworkDispatcher extends SimpleChannelInboundHandler<Packet> imple
             completeServerSideConnection();
         }
     }
+
+    public void completeClientHandshake()
+    {
+        state = ConnectionState.HANDSHAKECOMPLETE;
+    }
 }
diff --git a/fml/src/main/java/cpw/mods/fml/common/network/internal/FMLMessage.java b/fml/src/main/java/cpw/mods/fml/common/network/internal/FMLMessage.java
index edce8a5c00..2efc50785d 100644
--- a/fml/src/main/java/cpw/mods/fml/common/network/internal/FMLMessage.java
+++ b/fml/src/main/java/cpw/mods/fml/common/network/internal/FMLMessage.java
@@ -21,7 +21,8 @@ import cpw.mods.fml.relauncher.Side;
 public abstract class FMLMessage {
     public static class CompleteHandshake extends FMLMessage {
         Side target;
-        public CompleteHandshake() {}
+        public CompleteHandshake() {
+        }
         public CompleteHandshake(Side target)
         {
             this.target = target;
diff --git a/fml/src/main/java/cpw/mods/fml/common/registry/FMLControlledNamespacedRegistry.java b/fml/src/main/java/cpw/mods/fml/common/registry/FMLControlledNamespacedRegistry.java
index 9a28cf2dd8..83a38b5788 100644
--- a/fml/src/main/java/cpw/mods/fml/common/registry/FMLControlledNamespacedRegistry.java
+++ b/fml/src/main/java/cpw/mods/fml/common/registry/FMLControlledNamespacedRegistry.java
@@ -1,28 +1,27 @@
 package cpw.mods.fml.common.registry;
 
 import gnu.trove.map.hash.TIntIntHashMap;
-
 import java.util.ArrayList;
 import java.util.BitSet;
 import java.util.List;
 import java.util.Map;
 import java.util.Map.Entry;
-
 import net.minecraft.util.ObjectIntIdentityMap;
 import net.minecraft.util.RegistryNamespaced;
-
 import com.google.common.collect.BiMap;
 import com.google.common.collect.HashBiMap;
+import com.google.common.collect.ImmutableBiMap;
 import com.google.common.collect.Maps;
 import com.google.common.primitives.Ints;
-
 import cpw.mods.fml.common.Loader;
 import cpw.mods.fml.common.ModContainer;
 
 public class FMLControlledNamespacedRegistry<I> extends RegistryNamespaced {
     static class FMLObjectIntIdentityMap extends ObjectIntIdentityMap {
+        private TIntIntHashMap frozenMap;
         private TIntIntHashMap oldMap;
         private TIntIntHashMap newMap;
+        private ArrayList<Integer> frozenIndex;
         private ArrayList<Integer> oldIndex;
         private ArrayList<Integer> newIndex;
 
@@ -54,6 +53,18 @@ public class FMLControlledNamespacedRegistry<I> extends RegistryNamespaced {
             newIndex = new ArrayList<Integer>(oldIndex.size());
         }
 
+        @SuppressWarnings("unchecked")
+        void freezeMap()
+        {
+            frozenMap = new TIntIntHashMap(field_148749_a);
+            frozenIndex = new ArrayList<Integer>(field_148748_b);
+        }
+
+        void revertToFrozen()
+        {
+            field_148749_a = frozenMap;
+            field_148748_b = frozenIndex;
+        }
         void completeSwap()
         {
             field_148749_a = newMap;
@@ -91,6 +102,7 @@ public class FMLControlledNamespacedRegistry<I> extends RegistryNamespaced {
     private I optionalDefaultObject;
 
     private BiMap<String,Integer> namedIds = HashBiMap.create();
+    private BiMap<String,Integer> frozenIds;
     private Map<String,Integer> transactionalNamedIds;
     private BitSet availabilityMap;
     private int maxId;
@@ -114,6 +126,11 @@ public class FMLControlledNamespacedRegistry<I> extends RegistryNamespaced {
         add(id, name, superType.cast(thing));
     }
 
+    int swap(int id, String name, I thing)
+    {
+        field_82596_a.remove(name);
+        return add(id, name, thing);
+    }
     public int add(int id, String name, I thing)
     {
         if (name.equals(optionalDefaultName))
@@ -182,6 +199,25 @@ public class FMLControlledNamespacedRegistry<I> extends RegistryNamespaced {
         transactionalNamedIds.put(name,newId);
     }
 
+    void freezeMap()
+    {
+        if (frozenIds == null)
+        {
+            frozenIds = ImmutableBiMap.copyOf(namedIds);
+            idMap().freezeMap();
+        }
+    }
+
+    void revertToFrozen()
+    {
+        namedIds = HashBiMap.create(frozenIds);
+        idMap().revertToFrozen();
+    }
+
+    Map<String,Integer> getMissingMappings()
+    {
+        return Maps.difference(frozenIds, transactionalNamedIds).entriesOnlyOnLeft();
+    }
     void completeIdSwap()
     {
         idMap().completeSwap();
@@ -232,7 +268,14 @@ public class FMLControlledNamespacedRegistry<I> extends RegistryNamespaced {
 
     public int getId(String itemName)
     {
-        return namedIds.get(itemName);
+        if (namedIds.containsKey(itemName))
+        {
+            return namedIds.get(itemName);
+        }
+        else
+        {
+            return -1;
+        }
     }
 
     public boolean contains(String itemName)
diff --git a/fml/src/main/java/cpw/mods/fml/common/registry/GameData.java b/fml/src/main/java/cpw/mods/fml/common/registry/GameData.java
index 4d63bea631..f25b805186 100644
--- a/fml/src/main/java/cpw/mods/fml/common/registry/GameData.java
+++ b/fml/src/main/java/cpw/mods/fml/common/registry/GameData.java
@@ -214,7 +214,7 @@ public class GameData {
         }
     }
 
-    public static boolean injectWorldIDMap(Map<String, Integer> dataList)
+    public static boolean injectWorldIDMap(Map<String, Integer> dataList, boolean injectFrozenData)
     {
         Map<String, Integer[]> remaps = Maps.newHashMap();
         ArrayListMultimap<String,String> missing = ArrayListMultimap.create();
@@ -265,6 +265,46 @@ public class GameData {
             return false;
         }
 
+        if (injectFrozenData)
+        {
+            FMLLog.info("Injecting new block and item data from this server instance");
+            Map<String, Integer> missingBlocks = Maps.newHashMap(blockRegistry.getMissingMappings());
+            Map<String, Integer> missingItems = Maps.newHashMap(itemRegistry.getMissingMappings());
+
+            for (Entry<String, Integer> item: missingItems.entrySet())
+            {
+                String itemName = item.getKey();
+                if (missingBlocks.containsKey(itemName))
+                {
+                    FMLLog.info("Injecting new block/item %s", itemName);
+                    int blockId = blockRegistry.swap(item.getValue(), itemName, blockRegistry.get(itemName));
+                    itemRegistry.swap(blockId, itemName, itemRegistry.get(itemName));
+                    missingBlocks.remove(itemName);
+                    if (Integer.valueOf(blockId) != item.getValue())
+                    {
+                        remaps.put(itemName, new Integer[] { item.getValue(), blockId });
+                    }
+                }
+                else
+                {
+                    FMLLog.info("Injecting new item %s", itemName);
+                    int itemId = itemRegistry.swap(item.getValue(), itemName, itemRegistry.get(itemName));
+                    if (Integer.valueOf(itemId) != item.getValue())
+                    {
+                        remaps.put(itemName, new Integer[] { item.getValue(), itemId });
+                    }
+                }
+            }
+            for (Entry<String, Integer> block : missingBlocks.entrySet())
+            {
+                FMLLog.info("Injecting new block %s", block.getKey());
+                int blockId = blockRegistry.swap(block.getValue(), block.getKey(), blockRegistry.get(block.getKey()));
+                if (Integer.valueOf(blockId) != block.getValue())
+                {
+                    remaps.put(block.getKey(), new Integer[] { block.getValue(), blockId });
+                }
+            }
+        }
         blockRegistry.completeIdSwap();
         itemRegistry.completeIdSwap();
         Loader.instance().fireRemapEvent(remaps);
@@ -298,4 +338,18 @@ public class GameData {
         }
         return true;
     }
+
+    public static void freezeData()
+    {
+        FMLLog.fine("Freezing block and item id maps");
+        blockRegistry.freezeMap();
+        itemRegistry.freezeMap();
+    }
+
+    public static void revertToFrozen()
+    {
+        FMLLog.fine("Reverting to frozen data state");
+        blockRegistry.revertToFrozen();
+        itemRegistry.revertToFrozen();
+    }
 }