I have a 550 series,and I experience the same issue. I don't have Comcast,but I do have the Motorola DVR. I'm not sure it's our televisions. Unplug your cable box when you're not trying to watch or record something. Let it sit for a couple of minutes and plug it back in. This worked (for awhile)for me. Again,I don't see how it could be the television,but I could be wrong.
I just got the Samsung 42 inch plasma, 450 model. Beautiful set. I'm very happy with it.
But, as stated with the 850 in that lengthy thread, it is also having interference issues with the cable box (Comcast HD, Motorola, dual tuner DVR). It isn't all the time. It is mainly in the On Demand section, it won't recognize the arrow buttons. Or, it won't recognize the ff buttons while in the DVR.
I've read in the other thread that Samsung will repair it. I've also read the repairs make the picture worse.
Is there a remote that will definitely fix this? I've heard the Harmony remote does. That might be a safer fix.
Love the set otherwise, but this is a very annoying issue. I didn't read about it until after getting the set. I was planning on getting another model, but saw the Samsung in the store and thought it had the nicest picture for the price.