If you bring up a menu that is near the right side of the screen and pop up
a submenu that appears to the *left* of the menu, you have to hit the Left
key to go up one level.  Similarly, if the submenu has subsubmenus, you
have to hit the Right key to pop them up.  This is a bit confusing, and
perhaps it would be a good idea to switch the keys around if submenus do
not pop up in their expected location, e.g. to the right of their parent menu.