I think the big problem here is that the "upgrade" process is not doing what it's supposed to do, and in this case as said completely uninstall 4.8 before installing 5.0,
as 5.0 isn't an update for 4.8, it's a completely new program. I think there should be a sticky
on the forums and the web site to tell everyone that they should uninstall 4.8 manually, reboot and install 5.0 from scratch. It's a never ending story atm, with tens of posters experiencing tens of issues with the so called "upgrade" procedure. Also linking to
http://www.avast.com/uninstall-utility in that sticky would be a good idea
ps: I guess there's no prompt for a reboot when running the "upgrade" procedure, after V4 has been removed, and before 5.0 gets installed