Ok. So after a few hours of adventuring. Ive noticed that I have 2 duskfangs in my inventory, and I have no clue how the second one got there.
I did spend a bit of time in prison prior to finding out I had the second. Can't complain though. Just a mystery I'd like to solve.

It's a known glitch. http://www.uesp.net/wiki/Shivering:Dawnfang is the Wiki page for the item. Scroll down to the bottom of the page for specific details.