When using my new script Background Changer and when using a Hold or right-click to drop down menu and when the slideshow changes before selecting something - the menu disappears ! 
It does not happen with normal menus. It does not matter whether the fade transition is on or off.
UPDATE: seems to be only happening to the Groupby dropdown, not happening with the Flatview dropdown. The Groupby dropdown is a custom button, but it is also happening to the default Groupby menu in the View menu.