Failed IMAP Server upgrade

Today i tried to update my Mailserver from dovecot 0.99.x to 1.0alpha3. Unfortunately the update requires several changes to the config file. And after i modified my config file i noticed that the new version has a bug.

Oct  2 20:40:51 knut dovecot: imap-login: Login: user=, method=PLAIN, rip=213.225.30.218, lip=213.9.70.77, TLS

Oct  2 20:40:51 knut dovecot: imap(arved): file istream-raw-mbox.c: line 450 (istream_raw_mbox_get_body_size): assertion failed: (rstream->mail_size != (uoff_t)-1)

Oct  2 20:40:51 knut dovecot: child 98776 (imap) killed with signal 6

Luckily i had a backup and i am now happily running 0.99 again. Let's see if someone on the dovecot Mailinglist can help me with this problem.