dovecot - Jul 2011 - phantom new message notification

I've developed a phantom new message notification on a single IMAP
folder in Thunderbird.  I've deleted the Dovecot index files for this
problematic folder, and I've deleted the .msf file in the Tbird profile.
 Neither of which solved the problem.  The only other time I've run into
something similar was with CONDSTORE quite a long time ago, but that
affected all folders, not just one.

Any ideas?

-- 
Stan