I'm not sure why it is that when a player reports an in-game message it disappears from their inbox.

If a player wants to delete it, there is a delete button.

Perhaps it's to prevent multiple reports but I do think it's odd that it's auto-deleted from the player inbox.

Yeah, I don't think its a bug but it's not well thought out. Perhaps the report button should cease to exist after reporting it. Or it should link to a confirmation that it had already been reported.