I have this same issue, and like you lose all my work after returning to the PC and pressing space bar to wake up from stand by mode.
I have tried "unscheduling" the boot time scan, and have even let the boot time scan complete after reboot, neither option fixes the issue. Of course there is no support information for this issue anywhere ....
To me all free antivirus software are pretty much the same, and I will be uninstalling avast in favor of AVG now, as this search was my last ditch effort to remedy this annoying problem so that i can focus on work and more important matters. Antivirus software is supposed to be transparent, not annoying. Thanks for a good run Avast, and good riddance! :]