I don't know know that it has yet been mentioned, but it would be good to eventually allow control of notifications (email/on-site) for when a user has been included as the recipient of a private message.
luceos Another fun edge case for you, but may give some more insight into this issue… This appears to also happen when one has been included as a recipient in a message tagged with a tag that is hidden from all discussions. Clicking through to the tag does not show recipients until the discussion itself has been visited. Hope that his clear enough.