I believe that the regular search also indexes some categories/characteristics, for example: if I do a search for "butterfly" and narrow it to just jewelry, I get a ton of erroneous results for pierced/post-style earrings that take butterfly backs even though they don't use that word in the title. Just fyi, I'm sure there are a million other little peculiarities due to keyword usage and weighting of search results but it's good to be aware, the better to search (and list) effectively.