I like this new ListBox control. The combination of buttons and drag-and-drop functionality is nice.
I found one problem when dropping list items to the target ListBox. The drop position is relative to the items already contained in the target ListBox. This means that if the target box is empty I can not drop an item in it. Of course I can use the move button, but this is a little inconsistent with the preferred drop action.
I would suggest a default drop action that adds the dropped item as the new last item in de target box. This can be overruled by dropping relative to an existing item.