Have that problem from time to time.
My format usually is to blame as it goes to a "zoom" mode or some other format.
I reset the format to what I want and it seems OK.
Haven't been able to narrow down when/why this happens. My suspicion is it might have something to do with either a "ping" from DTV through the phone line, or a channel switching from an HD clip to a standard clip and back.
Can't remember if I had the problem before the phone line hook up or not.
Never used the phone line until I wanted to buy a movie and it wouldn't let me do it on-line. (My other standard DVR reminds me that it has been over 900 days since I last "checked-in" with DirecTV.) Then I discovered Caller ID on the HD-DVR receiver. Nice! I use it as a phone book now.
P.S. Good to hear from you!
When you say you reset the format, do you mean for your television, or is there another format menu for the cable box? The zoom +/- for the tv doesn't help the oversized screen format for FNC. For example, the other night we had to switch over to CNN to see the NH election results at the bottom of the screen. They were not visible on FNC.