dovecot - Sep 2013 - doveadm sync only creates directories, don't sync messages?

Running Dovecot 2.1.7.

I'm trying to migrate from an environment with mbox files to a maildir 
configuration.

I remove all vestiges of my maildir over in /var/mail

I put my old mailboxes in ./Mail and my old inbox in ./matthew.

I issue this command: doveadm sync  -u matthew at matthew.at 
mbox:./Mail:INBOX=./matthew

Initially it gave me errors about separator, so I set the separator in 
the inbox namespace to "/" explicitly.

Now that I've done that, and re-run it, over in the right place 
/var/mail, it creates "matthew" and a subdirectory "Mail".
That's it.
Doesn't take long to do it, either. But it doesn't copy any messages at
all.

I must be doing something wrong... but what?

Matthew Kaufman
matthew at eeph.com