I've also had the challenge on thread response, the challenge robustly message, usually followed by a "we have deleted several of your posts, keep this up and you will be banned".
Mumsnet hq need to work out which direction they want the site to go in, and then moderate accordingly.
Either delete and moderate properly, removing posts that are damaging to society Tommy small bollocks is great kind of things, or, they let the challenges stand. They can't tell you to challenge robustly, then remove you when you do, so if thats what they want, then posts need to stand.