Finally I was able to resolve the issue. I had to do close Thunderbird.
Delete the misbehaving folders on imap-server Maildir/Trash. Start
Thunderbird, did "Repair" on Trash folder after that and the files were
gone!
There's only one waisted "ghost" folder shown for renew subscription
(grayed out) that does not exist on imap-server. But it's not shown in
my Trash-Folder anymore! So that's a good success.
I hope deleting folders in future won't make the problem reappear.
Best regards
Gabriel Kaufmann
