[Dovecot] Thunderbird Search Folder failures

[Michael Durket]

In converting everyone at our site from UW-IMAP I've run into another problem
with Thunderbird users that I'm hoping someone can help me with.

The dovecot version I'm running is old (1.0.13 - we don't do production upgrades
that often but I'm perfectly willing to install a newer version). The affected 
Thunderbird users are running Thunderbird version 2.0023 under Windows. All
mail is stored in mbox format.

What appears to be happening is that searches looking for string matches in 
the message body don't work. I set up a test case with the affected user.
We created a folder that had 6 messages: 5 containing the string in the 
message body and 1 that did not. Then we set up a search folder
that looked for the string. Opening the Thunderbird search folder 
yielded no messages matching the search. A rawlog trace of the search
 in dovecot showed that dovecot had indeed responded that no messages 
were found (when 5 should have been).

This doesn't happen with UW-IMAP (version imap-2007e which I think is the
last version with bug fixes ever issued). Is this perhaps a known bug in 
dovecot that was fixed many releases ago and I should upgrade?