I'm having a similar issue with IE11. It definitely has something to do with the MouseUp handler when the cursor is over the drag handle. It seems like if any part of your draggable object is off the bottom/right side of the screen when you trigger a mouse up on the drag handle, it will snap the object back into the frame.
I'm having an even stranger situation with mine, where I have a "content" div (parent), and a "stage" div (grandparent). When you drag outside as described above, and you mouse up outside the container (leaving some of the drag handle in the container), when you click the drag handle, it ends up shifting the entire content div up-left, and shows the background of the stage div, as if you had scrolled, but both of these divs are set to **overflow: hidden**.