I discovered by chance while migrating some user email to dovecot, one of them had a mailbox called "Inbox" and my script migrated it to a Maildir called .Inbox but Thunderbird could not see it at all, even in subscription lists. I tested with my account and it looks like mutt CAN see it. This seems like a client issue so I'll just make my migration script rename anything called Inbox to avoid it, but I thought I would send a note incase anyone else trips on it.