Meanwhile, I reviewed the source code of aswUpdSvc.exe I think I’ve found the problem.

Here is a (hopefully) fixed version: http://cat.asw.cz/~vlk/aswUpdSv.exe .

The only caveat is the avast’s auto-correct feature that will cause the patched file to be soon replaced by the updater. But there should be enough time to check if it’s working (i.e. stop the service, replace the file, start the service, and shut Windows down. Is it fast enough? After reboot, avast will unfortunately replace aswUpdSv.exe with the original version from 4.1.335 distribution but that doesn’t matter…).