So I just received a useless reply from Avast tech support about this. I opened a ticket last night saying that since KB3000850 Windows Explorer freezes, windows won't cleanly shut down, etc. -- until I uninstalled Avast.
I suggested that Avast didn't break Windows, that Windows broke Avast -- but that nevertheless Avast will need to try to fix Avast to remove the incompatibility.
Here's the response I received from support - I replied and told him his answer didn't help, and that I was not getting a false-positive virus report but freezes/crashes/crap.
Hello,
this would be most probably the new malicious software removal feature from Windows. It is common that one security software is finding the positive threats in other security software`s database which contains samples of viruses, as every antivirus application do. So that is why is not recommended to use two different antiviruses on one machine, because there will be 100% conflicts and it can cause damage of your system. Do not worry Avast is 100% threat clean.
Best Regards
Albert Fiala