When I use the [e]dit command in mutt to edit a message in my folder (e.g. to add my own annotations to it), it deletes the old message and delivers the message I just edited as a new message into my mailbox.
Wouldn't it make more sense for mutt to just apply the edit to the message without having to re-create it, at least when the folder in question is a Maildir? I think that for running the [e]dit command on a message in a Maildir, mutt should just start vi with the message file as the argument and it doesn't need to do anything else.