Don't use Packet56 and clear client cache on world changes.

src/main/java/net/minecraft/server/EntityPlayer.java

@@ -167,7 +167,13 @@ public class EntityPlayer extends EntityHuman implements ICrafting {
             }
 
             if (!arraylist.isEmpty()) {
-                this.netServerHandler.sendPacket(new Packet56MapChunkBulk(arraylist));
+                // CraftBukkit start - don't use map chunk bulk for now TODO: fix this
+                for (Object object : arraylist) {
+                    this.netServerHandler.sendPacket(new Packet51MapChunk((Chunk) object, true, 0xffff));
+                }
+                // this.netServerHandler.sendPacket(new Packet56MapChunkBulk(arraylist));
+                // CraftBukkit end
+
                 Iterator iterator1 = arraylist1.iterator();
 
                 while (iterator1.hasNext()) {

src/main/java/net/minecraft/server/ServerConfigurationManagerAbstract.java

@@ -380,6 +380,8 @@ public abstract class ServerConfigurationManagerAbstract {
 
         // CraftBukkit start
         byte actualDimension = (byte) (worldserver.getWorld().getEnvironment().getId());
+        // Force the client to refresh their chunk cache.
+        entityplayer1.netServerHandler.sendPacket(new Packet9Respawn((byte) (actualDimension >= 0 ? -1 : 0), (byte) worldserver.difficulty, worldserver.getWorldData().getType(), worldserver.getHeight(), entityplayer.itemInWorldManager.getGameMode()));
         entityplayer1.netServerHandler.sendPacket(new Packet9Respawn(actualDimension, (byte) worldserver.difficulty, worldserver.getWorldData().getType(), worldserver.getHeight(), entityplayer.itemInWorldManager.getGameMode()));
         entityplayer1.spawnIn(worldserver);
         entityplayer1.dead = false;