I used a work-around for my website with the same problem. Although, I am making an e-commerce site for online ordering and the customer pays at the store. So instead of using just cash on delivery as the only option, I activated cheque and just changed the name to "Pay at store" and the description to "Pay with your preferred method when you pick-up your goods."
It seems that it doesn't read cash on delivery as a real option, so I just changed the description of cheque.
I don't know if this helps any of you but that's how I solved it