duplicate e-mails

I'm still having trouble with fetchmail. It fetches mail from five different POP3 accounts and drops in in my /var/mail/hans. Some mails are duplicated. Sometimes it would be all the mail in one box, sometimes a few here and there. I've verified that the mails aren't on the servers in duplicate, and don't get downloaded twice either. It just somehow doubles when being delivered. Any clues as to why this is happening? man fetchmail wasn't a lot of help, google mostly gave me links to fetchmail source (?) Thanks Hans