Same box, different TV - Samsung 40A650. Notice that the remote works after some "time" or after channels change is done via the box, or some other mysterious event.
Other posts have suggested:
TV "power saving" interference. I turned my power saving feature off, no change.
Honestly, I think there is some kind of "bug", and not interference because even when I jam the remote right next to the box's IR sensor, it won't work. But once it starts working, it works rfom then on.
I think everyone having this problem we have got to call comcast and keep having them swap our boxes until they work it up-stream (firmware?)