Please find vs2010 solution demonstrating this at www.messy-mind.net/temporary/TreeDemo.zip
Expand the Folder elements on the left treeview. Select Element 5 child node. Use the right treeview to change its ParentIndex to 1.
No change occurs in the left treeview. If you attempt to collapse Folder 2, the collapse/expand box vanishes. If you collapse/expand Folder 1, Element 5 does not show in it.
If you hit force refresh, the relation is cleared and re-added, the left treeview works correctly again.