I'm having a couple of odd problems with a simple mod rewrite .htaccess file.

My .htaccess file is as follows. You'll notice the rules are split into two groups. The first bunch of rewrite rules work fine, the second just go to a 404 page. The files they're redirecting to most definitely exist.

To add to the strangeness, the sitemap redirect sends it to sitemap.xml instead of sitemap.php!!!

RewriteEngine On
RewriteBase /
RewriteRule ^askben$ askben.php
RewriteRule ^contactus$ contact.php
RewriteRule ^privacypolicy$ privacy.php
RewriteRule ^sitemap$ sitemap.php

RewriteRule ^links$ links.php
RewriteRule ^articles$ articles.php
RewriteRule ^schools$ schools.php
RewriteRule ^business$ business.php
RewriteRule ^jobs$ jobs.php

Any ideas? Am I doing something very obviously wrong?