U++

My patch didn't solve the problem with repeated right mouse click.
Current solution works for the test case, but (new) issue is open for discussion, still.

But might be exists the possibility of stack overflow for the solution (second patch), because of possible long recursion.
The previous menu level checks apply in reverse, which accumulate with each new level.

Well, the "full" solution would probably had to use some form of PostCallback so that Execute is left before the new Execute is started. Anyway, for now I consider that sort of quirky, as perhaps things would not behave as one expects (that is, that the menu operation is performed before Execute exits).

With third patch the menu closes without the "tail" of previous menu (this is correct).
But after testing with MenuBarExecute application, I found, that destructors of MenuBar still accumulate, which causes the application to terminate for some number of executed menu in loop (in my case it was for n >= 985). This is also true for current (r5394) approach, but with many levels.