I think this facility needs improving. It nearly always comes up with threads that don't even include the words put in the search box. If it worked better, there would be a lot less repeat threads. Or is it just me?
Use Google Advanced search and place the ybw.com in the appropriate field. Google will then search only the YBW forums using your other search words. It is very effective. I had the same issue as well.
It is a bit rubbish but, meaning no disrespect to them, I wonder whether a publishing house's IT department is up to the task of writing a better search algorithm and incorporating it into the existing software. Note that they didn't write the forum, it's a standard off-the-shelf package they simply installed.