Hi sncooper,
Let's start off by figuring out whether it was a change to Fusion or a change to Mac OS that is triggering this. Could you try downgrading to Fusion 5.0.1 (again!) just to see whether the problem persists?
Regardless, you should probably start a new forum discussion for your issue instead of piling it onto this massively-overloaded thread. Make sure you also mention whether you're using your VMs in single-window mode, in unity or in full-screen, and the method you're using to switch between them.
Cheers,
--
Darius