[Dovecot] Can't delete sub-folder

[pch0317]

Hi list,

I have problem with deleting sub-folder.
I use thunderbird 8.0 as a client and dovecot 2.0.9 with imap protocol 
as a server. I use dovecot with tb-extra-mailbox-sep parameter. I use 
mbox mailboxes and thunderbird with *not checked* option 'server 
supports folders that contain sub-folders and messages' so when I create 
sub-folder I can choose between 'folders only' and 'messages only'.

When I try to delete 'parent' folder which contain 'messages only' 
folder, error message appear: [ALREADYEXISTS] Mailbox has children, 
delete them first. Ok, so I delete 'message only' folder first and try 
to delete parent folder, but the same error appear: [ALREADYEXISTS] 
Mailbox has children, delete them first.
When I list mailboxes from console I see inside 'parent' folder ".imap" 
folder. When I delete .imap folder from console and then delete parent 
folder from thunderbird, parent folder is deleted correctly.

Which application create this ".imap" hidden folder and how solve this 
problem.



Thanks