yes...for me also I was not always able to duplicate the problem. I did however duplicate it a couple of times and more importantly the customer was able to.
After looking at the Product_Results.php page the sql gets pretty deep, so I'm inclined to to touch it until I'm completely familiar with how it works.
Tell me, is there (I don't see any) server variables that keep data where the search would pull from? It seems (when I can duplicate the problem) that the search is keeping the last known search criteria or sql statement.
I've been able to search on the 605 or something else and the search works, but when I search on something different it reverts to the 605 search results or the "all" products results