OK I'm here again to update my own non-answer from earlier. I just swapped out the USB cable, and somehow it's working as desired now. All other things equal, only a new cable and now the 48v powers on and the devise stays connected with no red led lights, etc. That blows my mind, too, because the new cable i bought was the $4.88 job from walmart, just a 6' onn-brand printer cable. In fairness, the cable I was using before was 10', unknown brand.
But still...