[Typo3] typo3, realurl and 404

[Pawel Krawczyk (IDG)]

I've just came up to a problem with generating 404 not-found pages.
Google doesn't like websites which reply with codes other than 404 to
non-existent pages. That's good policy, but causes some problems with
Typo3 to achieve.

Using previous posts from this mailing list I've solved problem of
"return closest good page instead of 404" even with realurl installed.

However, I've come up to a problem which I can't solve because I don't
know which module is responsible for this behaviour. Specifically, my
website returns 404 for non-existent pages, but still returns 200 status
for SOME of them.

That's what Google checks. The page/file doesn't exist but website
returns 200 mainpage (wrong):
http://kabardians.com/GOOGLE404probea95361cb8d35071a.html

If you try you'll see correct 404 error:
http://kabardians.com/GOOGLE404probea95361cb8d35071a

This also doesn't exists and returns 404:
http://kabardians.com/laksjdlaksdj

This one doesn't exists BUT it returns 200 mainpage:
http://kabardians.com/laksjdlaksdj.a

As you see the difference is ".a" or ".html", whatever it is it's the
extension ".anything" that changes the error behaviour.

I can't find which module is changing this. It's not Apache's
mod_rewrite for sure, so it has to be either Typo3 core or realurl.

Any ideas?