[Dovecot] Thunderbird 3.1 unable to delete subfolder of Trash under mdbox

[William Blunn]

Thunderbird 3.1.9 over Windows 7.

Dovecot 2.0.11 (2:2.0.11-0~auto+41 from http://xi.rename-it.nl/debian/ 
source on 8 Apr 2011) over Ubuntu 10.04 LTS.

Trying to set up a Dovecot system with mdbox. But I also wanted to keep 
some Maildir. So I ended up with both mdbox and Maildir side-by-side and 
noticed an issue.

On this system, Dovecot's global mail location is configured with 
maildir:~/Maildir

I have a two users configured in a password-file passdb/userdb:

One using the Dovecot global mail location (maildir:~/Maildir)
the other with an override mail location (userdb_mail) of mdbox:~/mdbox

(The only other configurations different to the default were to turn off 
the default system password passdb and userdb, and enable my local 
password-file-format passdb and userdb.)

I have configured two IMAP accounts in Thunderbird 3.1.9, one to access 
each of the two users above.

The test procedure is:

In Thunderbird, create a folder at the top level (i.e. alongside Inbox), 
say "foo".
In Thunderbird, delete the folder just created.
This results in Thunderbird "moving" the folder to "Trash", resulting in 
a folder "Trash/foo".

Up to this point, both the Maildir and mdbox users behave OK.

Then in Thunderbird, delete the trashed folder "Trash/foo".

At this point, things start to happen differently.

With the Maildir user, the folder "Trash/foo" deletes successfully.

But with the mdbox user, Thunderbird pops up an error:

The current command did not succeed. The mail server for account 
<accountname> responded: Invalid mailbox name: Trash/foo/.

The folder does disappear from the Thunderbird folder pane, but if 
Thunderbird is "prodded" to refresh what folders it thinks are there, 
then the folder reappears. If we check the user's mdbox directory, we 
can see that indeed the mailbox has not been deleted.

Whatever I then do, I am unable to delete this folder in the mdbox user 
through Thunderbird.

The only way I have found to safely delete the folder is to use "doveadm 
mailbox delete", but this requires root privilege on the server, which 
is not really a practical solution.

It maybe a Thunderbird problem, but the question then arises: Why does 
it work under Maildir but doesn't work under mdbox?

Any ideas?

Bill