to put it in a different perspective, if your URL can be dynamically changed to another URL which does not reflect the actual keyword you programmed for your URL and still resolves as a 200 header found, you've got a problem.
Informative post Dusky. Let me understand what you have posted here. If there is an additional keyword injected in the URL, you mean it should take you to a 404 error instead of displaying a page?
I have a Wordpress blog where I tested example.com/keyword-here/?q=spam-keyword and see that while the URL in the address remains the same (with the ?q= part included), the webpage has however resolved to example.com/keyword-here/
Do you mean this is a problem?
[edited by: tedster at 2:56 pm (utc) on May 8, 2010]