Between the small delay of a moving off the opened submenu and back to a sibling if you click a radmenuitem the click is ignored unless you wait until the submenu is fully closed.  This results in the experience of the click not working after you scroll down the menu. Very easy to repro, only affect menuitems very near the opened submenu. Issue does not occur in WPF.
Attached is a visual example of a menu item that would not work if clicked