Help with weird URL parsing problem

I am an nginx newbie. Apologies in advance for stupid questions.

I am running Wordpress on nginx on a linode....I made the switch for performance, and I have been thrilled.

I have one problem -- my setup will not handle any wordpress URL containing the characters "php"

For example

http://www.mysite.com/this-url-contains-the-characters-php.html --> 404

or

http://www.mysite.com/category/php/post-slug --> 404

etc

Any URL on my site that contains the characters "php" in the URL results in a 404 error.

I am baffled (no doublt because I am a newbie).

To make matters worse, searching for help using "php" in the Google search query makes it impossible to find anything -- there is just so much stuff about using PHP with nginx that you cannot sort through it all....

Anyway -- can you guys think of something to check?

Open to ideas.

Thanks,
Mark