Are you sure you're not just using Forum search inside a thread or section? Here it works relative to where you are. If you are in the main index you'll be searching all threads of every section and you get a lot of sort and filter options.
It looks like they block spiders from all but forum-index and faq. Forum search is better because there isn't a big delay in results do to crawl-timeout.
On forums with broke search I actually just use javascript and a iframe to make my own search.