Summary:

If you have a some disabled and some enabled droppables the "over" and "out" events may not fire.

This line appears to be the culprit:

ui.droppable.js(210): if(this.item.disabled) return false;

The return false will signal $.each to stop iterating which will cause any droppables in the list, that occur after a disabled one, not to fire "over"/"out" events.

Possible Solution:

Change the return statement to just "return", and not "return false".