I would first like to say that I love the AJAX that I see when I go to unmanage a node. Keep the AJAX coming! Now on to the bug...
If you click in one of the time fields when unmanaging a node, and then click outside the field without making a selection, the drop down box doesn't go away. This does not happen when you click on the date field. In other words, when focus is lost on the time fields there isn't an event to make them disappear. The only way to make them disappear is to actually make a selection.
I'm not sure if this bug existed in earlier versions or not.