Defroster/defogger/hvac System Rear Window problems of the 2013 Ford F-150

Driving down the road at 40mph on the way to work this morning. Turned on the rear window defroster and about 2 minutes later, the driver side panel of the back tempered glass window spontaneously shattered. There is no evidence of any obvious defect to either side of the window. An impact wouldn't be possible given I was driving forward at 40 mph. I have looked online and seen message boards full of similar reports but don't see any recalls. I wanted to add my report to the numbers as this is ridiculous and I now have to pay $800 to have something replaced that definitely appears to be a known manufacturer defect.