Earl posted in the main issues thread that he forwarded this issue on to the guys at DirecTV so they should be aware of it now (if they haven't already).
And for the DirecTV guys: It isn't just Sunday Ticket. It's any sports subscription. And it also happens on the special events channel 95. And what happens on 95 is it doesn't "light up" right on time all the time so if the recording starts while the channel is still dark, I think this is when you get the recording that prompts to delete right after you start to play it.
Another possibly related issue is say you lose signal due to weather. From what I've read people get the "partial" recording in the history only when this happens.
So it seems the HR20 has issues when there is a loss of signal whether it be from a sports subscription channel going dark early then the end of a recording or not starting until after the recording starts or from a signal loss for whatever reason.
Hopefully you'll be able to find the issues.
At the least, allow the recording of nothing if there is no signal. It's ok.