Remove UUID fields in ForgeWorld when creating entities.

src/forge/java/com/sk89q/worldedit/forge/ForgeWorld.java

@@ -32,6 +32,7 @@ import com.sk89q.worldedit.blocks.BaseItemStack;
 import com.sk89q.worldedit.blocks.LazyBlock;
 import com.sk89q.worldedit.entity.BaseEntity;
 import com.sk89q.worldedit.entity.Entity;
+import com.sk89q.worldedit.internal.Constants;
 import com.sk89q.worldedit.internal.helper.MCDirections;
 import com.sk89q.worldedit.regions.Region;
 import com.sk89q.worldedit.util.Direction;
@@ -539,9 +540,13 @@ public class ForgeWorld extends AbstractWorld {
         World world = getWorld();
         net.minecraft.entity.Entity createdEntity = EntityList.createEntityByName(entity.getTypeId(), world);
         if (createdEntity != null) {
-            CompoundTag tag = entity.getNbtData();
-            if (tag != null) {
-                createdEntity.readFromNBT(NBTConverter.toNative(entity.getNbtData()));
+            CompoundTag nativeTag = entity.getNbtData();
+            if (nativeTag != null) {
+                NBTTagCompound tag = NBTConverter.toNative(entity.getNbtData());
+                for (String name : Constants.NO_COPY_ENTITY_NBT_FIELDS) {
+                    tag.removeTag(name);
+                }
+                createdEntity.readFromNBT(tag);
             }
 
             createdEntity.setLocationAndAngles(location.getX(), location.getY(), location.getZ(), (float) Math.toDegrees(location.getYaw()), (float) Math.toDegrees(location.getPitch()));

src/main/java/com/sk89q/worldedit/internal/Constants.java

@@ -0,0 +1,45 @@
+/*
+ * WorldEdit, a Minecraft world manipulation toolkit
+ * Copyright (C) sk89q <http://www.sk89q.com>
+ * Copyright (C) WorldEdit team and contributors
+ *
+ * This program is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Lesser General Public License as published by the
+ * Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License
+ * for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package com.sk89q.worldedit.internal;
+
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+public final class Constants {
+
+    private Constants() {
+    }
+
+    /**
+     * List of top level NBT fields that should not be copied to a world,
+     * such as UUIDLeast and UUIDMost.
+     */
+    public static final List<String> NO_COPY_ENTITY_NBT_FIELDS;
+
+    static {
+        NO_COPY_ENTITY_NBT_FIELDS = Collections.unmodifiableList(Arrays.asList(
+                "UUIDLeast", "UUIDMost", // Bukkit and Vanilla
+                "WorldUUIDLeast", "WorldUUIDMost", // Bukkit and Vanilla
+                "PersistentIDMSB", "PersistentIDLSB" // Forge
+        ));
+    }
+
+}