[ale] Thunderbird vs. Dovecot: "imap new mail checking"

[stevejunk at iintiip.com (Steve Tynor)]

I read my mail with Thunderbird 1.0.2 via IMAP on a FedoraCore3-hosted 
dovecot  0.99.11-1.FC3.4) server.

It all works very nicely except that "new mail" checking seems to be 
unreliable. I use procmail to deliver to a dozen or so mailboxes and 
have set up Thunderbird to monitor each of them for new mail. Sometimes 
it properly notices that a mailbox has new mail.  Often times, though, 
new mail will not be noticed until I click on a mail folder - then 
suddenly Thunderbird will notice that the folder has new mail. (and I 
can verify that that new mail had been delivered hours ago - long enough 
that auto check should have noticed).

I've googled for "new mail" bug reports for Thunderbird or Dovecot and 
haven't found any known issues.  Can anyone recommend how best to debug 
this?  Is anyone else seeing similar problems?

Thanks!
Steve