[Dovecot] Client behaviour with sieve

[Koenraad Lelong]

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.