I have a group of users using 6.5.4 mail template on R7 server.
They are having many instances where they see documents in their Inbox or All Docs view and when they try to open some docs they get the error message "Invalid or nonexistent document". They assure me that, and I now believe them, they have not deleted these emails.
Shift F9 will remove these docs from the view but they have not been deleted!
I have looked closely for a pattern but can see none. This affects internal and external mail, forwarded docs, with/without attachments.