Overlapping sortables, wrong drop target
I have a somewhat complex drag and drop scenario, that's revealing a bug in the jQuery UI Sortable code. This happens in 1.8.9, but I have reason to believe it may have existed in earlier builds as well.
Say you have two sortable targets, one above the other.
---------
Area 1
---------
Area 2
---------
As you drag your element around, usually the placeholder appears in the correct area. The exception is when you drag the element to the final position in either list. In that cass, there is a scenario where the item will appear in the wrong list, seemingly without fail. That is, if your element is hovering over area 1, the placeholder is in area 2, and vice versa.
If the areas have a scroll bar, and they are scrolled so that the contents of one 'overlap' the other (ie, if you took the scrollbars away, the content would overlap), then the placeholder ends up in the wrong Sortable.
One thing to note about this is that it seems to work both up and down the page. If you scroll Area 2 to the bottom and drag an item over Area 1, it'll appear in Area 2. In fact that scenario is easier to demonstrate, because you can actually see the elements in Area 2 move to accommodate their new friend.
The oddest thing about this is how consistent the behavior is. I would expect something more arbitrary, like if two nodes overlap, the first one wins, or the last. Instead it looks like Christmas; whichever is the most 'needy' list gets it, instead of the one most likely to already have it.
I think I could work up a repro case if that wasn't sufficiently clear, but I don't have a canned one to send at present.