I'm using the 24.0a1 (2013-06-15) build under Windows 7. I have a IMAP account with Fastmail.fm that uses a Cyrus server. The INBOX.Misc.DeveloperWorks , INBOX.Misc.Java.JavaRanch , INBOX.Misc.Java.Serverside, and INBOX.Misc.purchases child folders had been deleted several months ago. I expanded the Inbox.Misc folder hierarchy this evening and noticed those folders existed, in grey italic letters. The folder pane lists those folders both with and without safe mode. The folders are empty, are listed in panacea.dat, and do not exist in webmail.
The profile is shared by both daily and 17.0.6. If I run 17.0.6 it does not list any of those folders. None of those folders have mbox files (global search/indexing and offline folders are disabled). I suspect I could get rid of the bogus listing by exiting Thunderbird and deleting the *.msf files, and if that didn't work delete panacea.dat. However, I want to understand why this happens before I do that. One reason is that several times over the last couple of months I got a empty grey italic inbox folder as a child folder of the inbox. It went away for a couple of weeks whenever I deleted it. Each time I deleted it I used file -> compact folders since the automated compacting when it will save over 1MB never runs (most of my messages are short plain text messages with no attachments, mail.imap.expunge_option is set to 2 (expunge the deleted messages when there are at least 20 messages waiting to be expunged), and the inbox is automatically compacted whenever I exit).
I have several other accounts with different IMAP servers and they have never had this problem. However, the only other account that I think I've deleted any folders on in the last couple of months was gmail.
http://kb.mozillazine.org/Grey_italic_folders states "A IMAP folder will be displayed in grey italics if the folder has a \Noselect flag. Normally this means the folder can contain child folders, but not messages." A Cyrus IMAP server has no problem with folders that contain both child folders and messages.
As an experiment I right clicked on "purchases", selected Delete, and confirmed that I wanted to delete the folder. It did. I then tried to copy a message from the inbox to Serverside using Message -> Copy To. It doesn't list that folder in the folder listing (or any of the other grey italic folders). I then tried to drag and drop the message there instead - that failed as the mouse cursor never changed from a circle with a slash through it. I browsed the folder hierarchy in the Subscribe window and it listed all of the grey italic folders. So it appears that only the folder pane and the list of subscribed folders knows about those folders.
As an experiment I created a xyzzy child folder in Inbox.Misc. , exited and restarted. That new child folder is empty but is displayed normally. I deleted the folder, exited , and restarted. The deleted folder was not resurrected.
The sharing tab in the folder permissions normally says "You have the following permissions: Read, Write, Insert (Copy Into), Set Read/Unread State, Delete Messages, Expunge, Create Subfolder, Post". For the grey italic folders it says "You have the following permissions: Full Control".
Ideas? Is this a known problem?