Interesting.. before the 811, I had a Samsung OTA HD receiver, and it always synced it's clock to whatever time was being sent by the digital station. There were some stations that were several hours off.
I wonder if the 811 is doing the same thing?
Or.... it reminds me of the Cell Phone I used to have... it received time from the cellular network.. if you had no signal, it would keep time internally, but used a very low quality clock chip, as it expected to be able to update itself from the network. As a result, the longer you were out of signal, the more the clock would drift....
The same thing could be affecting the 811... it's not getting dish time signal while tuned to an OTA station, and it's own clock slowly difts. Then, when tuning back to a satellite signal, it corrects itself.