Hey all, hope you don't mind if I jump in. I purchased a 4270 about two weeks ago and although its not the specific model mentioned here its likely got most of the same guts.
I'm currently only using ANT A input for OTA HD only. No cable, no D*. About a week ago I had this exact same issue. The set had been on for about 5-6 hours (I was home sick that day, actually) and at some point the set just shut itself off and the blue light flashed a bunch of times. Unaware it might turn itself back on I pushed the power button (or maybe it was just coincidence) and it came back on. While I didn't notice anything having to do with video/audio/tuner was wrong, I immediately noted that the clock and guide info was a full hour behind. I checked to see if somehow the DST settings had gotten fubar'd but they were normal. So I took a shot and power cycled it and voila, the clock and program info was now correct. This would seem to be circumstantial evidence that the guide getting corrupted somehow does have something to do with this issue.
I haven't had this problem again, but I also haven't had the set on for that long since then either. I have seen this issue reported by other owners of the 4270, also so I don't think its specific to just the 5070/1140.
I sure hope a solution, or at least an explanation, eventually makes its way around. So far for me this minor issue certainly doesn't outweigh all the other truly fantastic features of this set.