[Dovecot] rc23 Problem - Assertion Failed

Feb 27 14:17:46 wurfel dovecot: imap-login: Login: user=<USER>, method=PLAIN, rip=127.0.0.1, lip=127.0.0.1, secured Feb 27 14:17:46 wurfel dovecot: IMAP(USER): file mbox-sync-update.c: line 387 (mbox_sync_update_header): assertion failed: (ctx->mail.uid != 0 || ctx->pseudo)

This is happening for dozens of users. Anyone have a suggestion of what to adjust? It was happening somewhat less frequently in RC22, and I believe the line number was in the 4hundreds there...