D&D when using DelegateModel with QAbstractItemModel produces some strange result

In a simple Quick application using QAbstractListModel and DelegateModel shows some wired behavior when drag and drop operation is performed and the list is sorted.

Attached simple application can be used to see the behavior:

Steps to reproduce:
Case #1:
1). Drag some items in the list
2). Turn on Sort button, note that the items in the list will do some weird things, overlapping each other
3). Turn off sort, note that the list returned to its previous order
4). Turn on sort, note that the list is now sorted correctly
5). Subsequent clicks on the sort button work as expected
 
Case #2:
1). Restart the app
2). Drag some items in the list
3). Turn on sort button
4). Turn off sort button
5). Drag some items in the list, note that dragging no longer works correctly