[Dovecot] Dovecot is emptying Maildir folders

[Alexander Johannes]

Hello,

i have a annoying problem with dovecot after updating to 1.1.14.

Dovecot seems to empty all cur/ and new/ Folders in the Maildir of a 
particular user several times a day (3 times so far). It leaves only 
unread messages in their place. All Index-Files are getting updated and 
reflect the "empty"-State of the Mailbox.

A quick look over the logfiles reveals nothing which seems to be 
relevant to this malfunction. The error_log is empty for the relevant 
timeframe.

There is no Expire/Expunge-Plugin running.

Fortunately i have a hourly backup-snapshot to restore the Mailboxes, 
but this is obviously no solution.

How can i debug this problem? Any advice is welcome.

System: FreeBSD 7.1-RELEASE, dovecot-1.1.14, dovecot-managesieve-0.10.6, 
dovecot-sieve-1.1.6 (all installed via the ports-tree), exim-4.69_3

Clients: Thunderbird, Mail.app both IMAP only


Regards,

Alex