I reported this against rc7 and rc8, and still see it occasionally. (I'm running the rc8 that comes with Fedora 5).
It is always associated with this message in dovecot.log:
dovecot: Oct 23 19:26:17 Error: POP3(user@domain.tld): mbox sync: UID inserted in the middle of mailbox /var/mail/vhosts/domain.tld/user (12 > 4, seq=2, idx_msgs=5)
Once this happens, dovecot will refuse to clear out the mbox file when the user retrieves email via POP. Each time the user logs in to retrieve mail s/he gets everything in the mbox, which continues to grow. The only fix I've been able to find is to manually delete the mbox file.
I'm using postfix as the MTA.
-- James Garrison Athens Group, Inc. mailto:jhg@athensgroup.com 5608 Parkcrest Dr http://www.athensgroup.com Austin, TX 78731 SKYPE callto:jhg-athensgroup (512) 345-0600 x150 PGP Key ID: 0x22E8DA2A