Yes, it is hurting the SEO. For more information than you might ever wanted to know about this, see the comprehensive blog post that Dr. Pete (an SEOmoz associate) posted last night at http://www.seomoz.org/blog/duplicate-content-in-a-post-panda-world. That should be a good starting point to understand why you don't want this happening, and how to start to fix it. The comments touch on case sensitivity as well, even though he didn't include that in the post itself.