Okay, I am coming back to check on this post a few weeks later to see if there has been any news...
I have to apologise about being so quick to point a finger at Avast! and thinking that it´s an Avast! problem, but after my last post I also got the same "leftover/ghost" problem with Windows Explorer menus, and items just staying there on the screen.... so it wasn´t just with Avast!.
I also tried the Kerio deinstallation, and voila! It worked! Not only did it get rid of the ghost problem, but also the problem I had with Avast! not starting up automatically after doing a memory scan.
Anyway, I´m off to look for another firewall now (I heard somebody mention Comodo, so I´m gonna check that one out).
Thanks again for solving this mystery!

Barbarella aka Gothic Barbie