Well I tried this on another machine with the Unity desktop, using a new user
account. The result is that I can still see the menu problem, but not the
tooltip problem. In fact the tooltips look quite different on Unity, and are
using transparency effects, so perhaps that is why. Another slight difference
- if I leave the pointer stationary over the menu item, then after 3 or 4
seconds the sub-menu finally appears - with fvwm/no window manager this does
not happen, and the menu remains absent until the mouse is moved.
Anyway, here is another video to show the menu problem under Unity :-
http://youtu.be/e1s2RXsqJo0