Custom 404 Asp Page

I created my own custom 404 handler and it works, so when I put in

http://www.domain.com/badxxx.html
it produces the correct 404 error and you see
http://www.domain.com/badxxx.html in the url still which is fine.

But when I put in
http://www.domain.com/asdf

it redirects to
http://www.domain.com/index.html

it gives a 302 (moved temporarily) as well as the 404 error.
Why does it do this for not .html files? I dont redirect it at all, and am
using
thestring = Request.ServerVariables("QUERY_STRING") to get the url

but thestring sometimes does not display the asdf depending what I do after
this command, very odd.

does anybody have anyideas as to how to preserve this
http://www.domain.com/asdf in the url and avoid the 302?