The functionality of treelist with drag&drop without autosync and without batch saving, at the end of the drop the change is not saved.
There is available a hack in the forum
For me this is a bug because I would expect for the change with drop to be automatically saved but it seems that for your support it is not. I understand that all the other changes are saved by the user with a button but the drag&drop does not have a button for it.
So if you do not want to implement this at least add a warning in the drag&drop demos page about this and provide the hack from the forum link or something so that others can know that they have to apply the hack in order for the drag&drop change to be automatically saved.