i received a hr21 replacement receiver back in october 2012. about 3 weeks ago when i change the channel, the picture freezes on the old channel but i get the sound from the new channel. called tech support and they had me change a couple of settings, red button reset and it worked for a while. last week the same thing began happening. called tech support again and they had me do a red button reset and it worked again. changing the channel by using the guide, up/down button or entering the channel, same picture freeze. they want me to call when it happens again. is this a sign of a bad receiver?