ActionScript 3.0 :: Xml AppendChild Goes Nuts?

when copying nodes from one XML object to another using appendChild(), sometimes the copied nodes aren't put at the end of the XML object. I've added a file to test this:

Put a number into the field, ranging from 1 to 3, and click addNode. It copies a specific node (FileID = 1,..3) from one XML object to another, and trace shows the result. If I add 1,2,3,1,2 consecutively, then the last node '2' isn't added at the end of the new XML object, but somewhere in between.
 
I did find a work around by converting the node to a string and then appending that. But the fact that appending an XML node doesn't always put it at the end of the XML object puzzles me. It looks like a bug, doesn't it?