1. Go to
https://bitcointalk.org/watchlist_posts.php and click "Do it".
2. Make sure that replied-to threads are automatically added to watchlist (I think this is the default but doesn't hurt to check).
3. Unwatch all unwanted threads.
4. Forget that "Updated Topics" ever existed. Use the watchlist.So the only solution is "Forget that "Updated Topics" ever existed. Use the watchlist."
Why not have the entire "Updated Topics" as an option removed already.
I even went as far as to ignore the OP, yet there it is in my "Updated Topics", grayed out as if that's enough.