I've tried disabling the skins, and that had no effect. I also tried the following mega-me skins - Battalion 23, Green Eyes, Tekno, and Z. Again, nothing.
I couldn't find any menus in the mini-me skins.
Maybe it would help if I tried to explain the problem more clearly.
The problem is repeatable and predictable.
It affects all the menu tabs that have menus (and excludes the Help tab in Media File Properties which does not have a menu).
It locks up the last menu opened. For example, if I select Settings/Options/OK, and then back on mega-me, I click on Settings again, the menu won't open. Clicking on Settings again opens the Settings menu.
After Settings/Options/OK, if I click on any other menu, the menu will open.
That said, I'll install the latest MJ release sometime in the next week, hoping that the reinstallation will clear the problem... (unless you suggest otherwise).