[Dovecot] IMAP inbox: cannot delete tagged messages or change their tag

[Epimedia]

Hello, a bit of a problem with Dovecot. Version is 1.0.15 and is a 
default install (no changes to config) from FC8 repository... except 
that Dovecot is configured to use Maildir

I have a user on the system who uses the tags in Thunderbird (Important, 
Personal etc). When she tags the messages they cannot be deleted and 
their tags cannot be changed.  When deleting a message from the IMAP 
inbox it momentarily disappears and moves a copy to the Trash but when 
the IMAP inbox is reloaded the message reappears. The same happens when 
I try to change a tag: it comes back with the previous tag.

Untagged messages can be freely deleted. Also, this problem does not 
happen if the messages are in a IMAP folder. They can be freely deleted.

The problem seems specific to Dovecot, not Thunderbird, as I am able to 
tag and delete messages in another IMAP account. Also, accessing the 
same IMAP account using OS X Mail the messages come back after deleting 
them.


Where should I start looking for a solution to this problem?