title: popup menu calling for update of all menus on each keypress
body: <p>I'm creating a pop up menu programmatically and updating it with the delegate method menuNeedsUpdate:(NSMenu *) menu and then displaying it using the popUpMenuPositioningItem:nil atLocation:mouseLoc inView:nil method.</p>
  
  <p>It works fine as far as mouse control is concerned. However, when using the keyboard (letters or arrow keys), I've noticed that it calls menuNeedsUpdate: for everything, the root menu and submenus. This is quite inefficient and makes using the menu via the keyboard sluggish.</p>
  
  <p>Why is this happening? Any way to circumvent it or stop it?</p>