my TB shows one unread mail at the folder name, but there isn't any. It's via imap, but even at gmail.com i don't have any unread mail. (It started yesterday with TB9.5, but remained with update to TB10.)
See it here: unread mail error (with menu -> view -> display -> show only unread messages, so you can see, that there is no unread mail in that folder)
I have no experience with IMAP so I can't help you there, but here are some other possibilities/suggestions:
- Check whether View -> Display -> All Messages is selected - Check below the message list whether you have a tab that is selected which does the same thing as above - Run Folder -> Maintenance Center and Check Integrity/Repair that folder - Delete the folder and create it again (I'm assuming there are no messages in it anyway)