We did change the behavior for the collapsing of the menus. The old behavior was to close the menus when the user moves their mouse away, however there was a bug that often resulted in a menu that would not disappear, as a result we now close any open menus if the user clicks outside of the menu area or if they move their mouse outside of the menu area.

If the WebPart is custom I would recommend making some changes to it so the combo box does not show outside of the menu area. If it is one of the standard WebParts please let me know so I can open a new issue.

Thanks,
Alan