Classified ads are only available for a finite amount of time after they're posted or bumped with a new post, so the ad you're seeing from the main thread view may no longer be available and there may not be a newer ad posted in that forum to take it's place in the main thread view.
Just a heads up that we're actually going to be phasing out the forum classifieds in coming months in favor of www.cothclassifieds.com, so feel free to check there for listings too.
If that doesn't appear to be the issue, please let us know.
I will check out the new link, but its not that I can't see the main thread, its that I can't see ANY posts. I click on "Horse Apparal" and there are no posts at all. Same for all the other topics. (but perhaps you are saying if there are no current posts nothing shows up...)
In any case, if you are creating a new place to look I will not worry about it....