Well, there are a few things we can try, since it works fine on the other v7.6.1.1 installs I've tested.
What browser are you using? Version? Are other users experiencing the same problems? What browser and version are they using?
1. Have you cleared your cookies from your browser for your site?
2. Have you cleared the cache on your forum?
3. Could you go and edit the forum and save the page with the show all threads option selected, and try again.
4. Could you remove any 3rd party additions to the configs to test, its possible that an included bit of HTML or external JavaScript may not be terminating correctly and could be overriding the setting when you visit the page.
5. Is all of your 3rd party code up to date? Providers commonly update their coding over the years and older coding can break over the years; providers such as google adsense, google analytics, ebay, amazon, etc.
Also, your link isn't applicable at all to anything recent; it's for UBB.Classic v6, which was in Perl, and was coded by a completely different developer (Charles Capps).
