[Dovecot] Client behaviour with sieve

Hi,

I have a working dovecot imap-server, with sieve. I find it odd that my mail-clients (Thunderbird 2 and 3) don't report anything that's new in the folders. What I mean is this : Postfix get's a mail and hands it over to dovecot's LDA and sieve moves it to a folder. When I log in with Thunderbird, I see new messages in my Inbox. But that message that was moved to a folder is "invisible" until I click on the folder. Then Thunderbird sees there are new messages in that folder and reports the number of new messages and makes the foldername bold.

Is this the expected behaviour ? Or did I configure something wrong ? Thanks for any clarification.

Regards,

Koenraad Lelong.