It seems that the Yamaha 796 actually is a Panasonic! It does not respond to the Yamaha discrete codes, instead it responds to Panasonic codes. The Panasonic discrete power off code indeed turns off the unit, actually turning it into a state of trance where you have to manually turn the unit on/off a couple of times to make it work alrigth again... I've heard about Panasonic DVDs with the same problem, unsure of which models. My player is region free (hardware fix) which I suspect could be the cause of the strange reaction.

Seems I have to use the play+toggle off combo:(