The playback on purchased or streaming movies on demand does not allow for full screen. Unfortunate given good picture quality but a lot of wasted screen space.
I have escalated your issue to the Comcast Team available to these forums. Check back often for a reply in this thread or via Private Message from a Comcast Official Employee.
I and look further into this issue. I'd like to check a few things on the backend to see if we can get this resolved. In order assist you, please send me a private message verifying your first and last name, the phone number, street address, and the account number associated with your services.
To send a private message click on my name "ComcastChe", then click private message me.