Remove tile entity tags for signs and command blocks

src/main/java/org/bukkit/craftbukkit/inventory/CraftMetaTileEntity.java

@@ -20,7 +20,10 @@ public class CraftMetaTileEntity extends CraftMetaItem {
         super(meta);
         this.material = material;
 
-        if (!(meta instanceof CraftMetaTileEntity) || ((CraftMetaTileEntity) meta).material != material) {
+        if (!(meta instanceof CraftMetaTileEntity) 
+                || ((CraftMetaTileEntity) meta).material != material
+                || material == Material.SIGN
+                || material == Material.COMMAND) {
             blockEntityTag = null;
             return;
         }