[Dovecot] Mail.app message numbering for deleted messages

I'm having a strange problem that appeared when I upgraded from .99something to 1.0alpha3 and then disappeared for a while and then re-appeared when I upgraded to 1.0alpha5.

I am using mbox and IMAP in Apple's Mail.app to read my mail. When I delete a message in Mail.app, the message gets marked as deleted in the spool and it disappears from the mail listing in Mail. However, the message number does not change until I either manually flush the deleted messages through mail, or I go offline which deletes the messages from the spool.

I have mbox_lazy_writes set to 'no' but this didn't seem to have any effect on the behavior. I never saw this type of behavior with UW-IMAP either, which is what I migrated from.

Thanks.