It would be helpful...but I dunno. (Tomorrow dons dunce cap.) We get frequent power outages here, or maybe it was a cosmic ray.
Yep...got it recalibrated and it's good to go. .... .... until .....
One possibility is that when I checked the rears...there may not have been much or any signal going to them. I even shut down all the speakers but the rears, just to verify. It's entirely possible, though doubtful, that what I was playing at the time was sending little or no info to the rears.