Scrolling breakes draggable element.

1. Open http://plnkr.co/edit/sQqhYVlZwd2VxGTGoEA8?p=preview in browser window small enough for scrollbars to appear.
2. Scroll preview area, while draging yellow rectangle, either by draging rectangle to border or with mouse wheel.
3. Yellow rectangle moves away from cursor, at some point it freezes.
