[Mac] handleOnMenuValidation may not be called when using system menu bar

Start simple test case attached.

1) If you invoke the Action menu item using the menu bar :
=> the onMenuValidation event handler is invoked => OK
Then, if you invoke the Edit menu using the menu bar :
=> the onMenuValidation event handler is invoked again and the undo menu item is updated => OK

2) Now do the same but using accelerators.
If you invoke the Action menu item using the keyboard (cmd + A) :
=> the onMenuValidation event handler is still invoked => OK
Then, if you invoke the Edit menu using the menu bar :
=> the onMenuValidation event handler is NOT invoked and the undo menu item is NOT updated => BUG
Invoking a second time works.

Note that if you do not use the system menu bar, then there is no issue.
This is a regression in 8u20.