[Dovecot] Dovecot failing silently on startup

I'm puzzled... I'm running the Debian package of Dovecot 0.99.10.4 on a Debian (testing) server, and it's basically doing nothing on startup for an extended period. After a while (maybe 10 minutes or more) it all suddenly starts working, all without logging anything untoward.

All the dovecot processes appear to start OK, and 'Dovecot starting up' is logged to the syslog. If you telnet to an IMAP or POP3 port at this point, it will successfully connect but there's no response (i.e. no '* OK dovecot ready').

Nothing else on this server is failing in this way; e.g. Apache and PostgreSQL are running fine throughout this period.

Has anyone else seen anything like this?

Cheers,

Julian.