I am using MC20 to act as a PVR, and I have a Hauppauge dual tuner card. It all appears to work fine - I can record two shows at once, and can watch a recorded show while those shows are recording. The issue occurs when I try to watch live TV when one (or both) tuners are recording.
Let say both tuners are recording and I try to watch live TV. A warning will come up - as it should - telling me what tuner #1 is recording, and whether I want to stop that recording to tune to my live TV channel. However, no mention of the second tuner and what it is doing. If I go in and manually stop the second tuners show recording, and go back and try to watch live TV, I still get the message that I have to stop the first tuner to watch live TV - even though the second tuner is available. IMHO, the warning message should come up and show both shows that are recording, and let you pick the one to stop.
As a side note - when looking at subscribed shows - and sorting by priority - if the priorities would ascend or descend on priority rather than alphabetically.