You can test it here: http://demo.sproutcore.com/drag_list/.
How to reproduce:
I've tinkered a bit with a code of SC.CollectionView. I guess the problem is in this line " if (i < idx) idx--;": (line 2998):
if (i < idx) idx--;
Though my fixes resulted in other bugs of the same nature.
These turned out to all be problems with the implementation of the demo.
In the delegate method collectionViewPerformDragOperation it removed objects after inserting them, so this needed to be changed to removing objects first and then inserting them in the proper new place. It also failed to allow the REORDER drag operation, by implementing collectionViewValidateDragOperation.
I'll be pushing an updated demo to the Showcase in the future.