Birthday's appearing twice in calendar app after adding to contacts

Hi all,

I recently started adding birthdays to my contacts on my phone. After doing this, each birthday appears twice in the calendar app (on the birthday calendar with gift icon). This also creates a duplicate of that contact in my contact list. These duplicates do not appear on iCloud.com, just my phone. Any ideas on how to resolve this?

PS - Using iPhone 4 running iOS 5

Thanks!