Apparel products "cross" categories in adv search

Obviously I'm doing something wrong, but every apparel product that I add seems to have a problem with regard to advanced search. The problem is this:

We sell musical instruments. Let's say for example that I have an apparel product set up for a series of drum heads (based on size). That product should appear under percussion categories. When I do a search limited to, say, Electric Guitars, the search performs as expected except there is that confounded drum head SKU.  (and every other apparel SKU for that matter.)

I'm currently running 3.12 and I don't think I should upgrade prior to the busy shopping season. Any ideas on what I'm doing wrong?

Thanks,
H.L.

http://www.alpha-music.com

Thanks. Here's a simple one: I'll do an search on the "Keyboards" category (idCategory=1442). I'll limit the search to between $150 -  $300. It yields 5 results, of which, only 2 are actually in the specified category. The other 3 are all apparel products.

Here's the query:
http://www.alpha-music.com/ProductCart/pc/showsearchresults.asp?idcategory=1442&idSupplier=10&priceFrom=150&priceUntil=300&sku=&IDBrand=0&keyWord=&customfield=0&SearchValues=&resultCnt=100&order=2&Submit.x=48&Submit.y=12

Thanks,
H.L.