Edits on flagged posts always create a revision. This helps moderators to understand why a user (or in your case, the system) flagged the post. If the reason why the post was flagged is removed in the edit and you couldn’t check the original version, how could you judge if the user flagging the post was right?
That makes sense, thanks for the explanation. I still think of users flagging posts and the system flagging posts as distinct functions, but it makes sense that they are handled the same way.