Dragging to a scrollable region

I have a div which contains a list of elements. Each element can
receive other draggable elements. The div is scrollable to accomodate
longer lists as I want a footer below the div to remain visible at all

When scrolling is not enabled (short lists), the drag and drop works
fine. Once scrolling is enabled though (longer lists) I find that I
have to drag elements to what would appear to be the absolute
coordinates of the target "receiving" element - that is, its position
if scrolling were not enabled.

Help appreciated.

After some more searching and testing, I have found a solution.
Setting "includeScrollOffsets" to true in prototype.js fixes the

Still, I would be grateful for any other thoughts on this. I'd rather
not change prototype.js directly if possible.