“My early Sangean HDT-1 tuner appears to…It sounds a little goofy, but it does switch to AM stereo after it has been tuned to KBPS for a few seconds.”
My Accurian does too noticed that when I actually could get an AM stereo station in my area. Sadly that is no longer true and I could be in the process of hunting down my own C-QUAM transmitter soon to fill this void. It would only be 100 mW and part 15 legal though. Can’t get KBPS during the day as I am relatively far from the Portland metro area at about 65 miles and their signal is riddled with interference from other AM stations.