SA 3.0 - USER_IN_BLACKLIST false positive?

[Mike Zanker]

Today I received a virus (Gibe-F) from an unknown e-mail address - it 
scored over 100 because of USER_IN_BLACKLIST. Now, I don't have any 
blacklists defined anywhere - in fact, SA is run only by MailScanner as 
user mail.

So, this seems to be a false positive. Anyone else seen it happening?
Thanks,
Mike.