Rewrite Problem

Hi, I setup my wordpress so that post links are of the form: http://www.domain.com/post-slug.html

However, when I go to any wordpres Page,
http://www.domain.com/page-slug.html, it redirects immediately to
http://www.domain.com/page-slug/. This is not in my .htaccess file, so must be a WordPress thing. Any ideas on what is happening?