Are you logging in as MTO or as mto? Scream's security fix has the side effect of not letting you edit your post if your username say has uppercase characters but you log in with lowercase letters (or vice-versa). I haven't checked to see if it was fixed, but I bet that's the problem.
If so, that could be fixed pretty easily, in that routine just have it convert the username to all lowercase (both the one you're logged in as, and the one who made the post). Then they should match either way.
