Post functioning like a Page

I build a theme to host the glossary – http://www.gartner.com/it-glossary/, where each term is a post.
Example: http://www.gartner.com/it-glossary/application-management

The Page object in the theme has the logic to display posts by a letter.
Example: http://www.gartner.com/it-glossary/a

I’m having a problem with one post – ITIL. If the permalink for this post is ITIL, WordPress seems to treat it like a page. If I change the permalink to anything else like ITIL-2, it works fine.

Any idea why WordPress would treat a Post as a Page?

Please help!