[wp-hackers] did I stumble across a bug?

[Foolish Visions]

I'm just curious if this is a bug, or something else.

I'm creating a custom search form, and it passes variables into a hidden input filed that contains a comma-separated list of category IDs. it seemed to be working just fine (searching in the categories I've designated) until I came to a search where I *knew* that certain posts should show up from between two categories. I then realized that even though my hidden input field contained the proper format (and the category ID's were being passed as they should to the query), the query was only looking in the first category ID instead of all of them.  

So, for instance, if I have 'input type="hidden" name="cat" value="1.3.5" '

the values of 1, 3, and 5 are being passed (as evidenced by the URL string - it contains "cat=1,3,5") - but it's only searching category 1 and ignoring 3 and 5.

Is this normal behavior? or a bug? or what? Everything I can find says that the input field (as I have it) should make the query use all three category IDs, but it's not. It's passing (even when I print_r the query vars, they show up as expected), but not using.

Anyone know?

~Shelly