Cyrus Imap ghost folders can't be deleted
I'm running Cyrus Imap 2.1.22. For quite a long time, I've had a series of nested folders and files that can't be deleted. I have tried rebuilding the index and the mailbox, no no avail. I have permissions to delete on it.
My client is Thunderbird 16.x. I have removed a bunch of files on the client side, but even setting up a new computer brings down these ghost files and folders, so I don't think this is a client issue.
I'm trying to understand why this happens but how to really get rid of them. I know I can just back the account up and delete, then create a new one (which I'm about to do), but that's a last resort.
Anyone else run into this odd problem?