It has happened a couple of times in the past, too.
Last time, it was Kasperky (if I remember correctly), about a year ago.
Once, it even happened to Avast (I think that was in 2001).
The problem is that the VB cleanset is not maintained too well - and sometimes, some questionable files slip in. This time, the files that avast was detecting were tools for adding the current user to the admin group, with the aid of a security hole in a Windows component. These were not false positives from avast - avast was detecting them intentionally (they were part of our database of samples). Strange that no other AV actually reported them as malicious...