fixed element leak across chunks

Scripts/Chunk.cs

@@ -138,6 +138,9 @@ public class Chunk {
         if (what.Chunk != swapTo.Chunk) {
             what.Chunk.RemoveFromChunk(what);
             swapTo.Chunk.AddToChunk(what);
+
+            swapTo.Chunk.RemoveFromChunk(swapTo);
+            what.Chunk.AddToChunk(swapTo);
         }
 
         Element temp = new Element(what);