I have a menu with vertical orientation, when I use mouse to navigate in the menu I have no problem. But if I open a menu that has a submenu (Accounting in this example) with a short cut key (Alt+A) I have difficulties when using Down Arrow key to navigate to the next menu item inside the submenu popup.
This is not an accepted behaviour. I have noticed that if I leave my mouse pointer in the place that the submenu popup opens and open the menu with a shortcut key there won't be any problem using Down Arrow key to move down inside the popup.