Very strange off-air (ATSC) tuner problem in HR20-700 ?

I have a very strange problem and hopefully someone recognizes this, or maybe can confirm how the off-air tuner works on the HR-20-700. 

(This is the model with the built in ATSC tuner)

I can't record two HD off-air ATSC channels at the same time, or if I am currently watching an off-air channel and attempting to record another off-air channel with the 2nd tuner. 

When the receiver attempts this, the channel is recorded but is it completely blank (no audio/no video/black screen recorded) 

once this happens, I lose signal for that specific channel from that point on - so any additional recordings on this channel will show up as "No signal detected"

The only way to regain the signal for the failed recorded channel is to manually go back to the System Setup for Antenna, Edit Channel list, perform a Signal Test and get a signal level for that channel.  Once a signal is detected in the test screen, I go back to that specific channel and it can now be received properly.  Until, it attempts to record another off-air channel while recording or watching an existing off-air channel and the problem occurs again

Has anyone else experienced this problem?

Could I have a defective ATSC tuner?    Recording 2 different DirecTV channels off satellite work perfectly.

When I check the signal on off-air channels, I get a typical 80-100% signal quality on tuner 1 on channels that are local to me, and the 2nd tuner always shows some sort of quality from 50%-100% even when it is tuned to a channel I don't get over air.  I am not sure what the 2nd tuner is picking up, or if this is normal.