Just registered to say that is something I've noticed on my Audi A3 1.6Tdi (2017) Sport Stronic
After reading this I understand the lack of consistency of the driver Select. I have a theory about this "reset" for the dynamic throttle to D after an ignition cycle, despite the of the cockpit showing efficiency mode and the prefix for the gear number letter should be E instead of D as shown.
As stated by "silus" this could and should be some kind of safety feature, but I don't agree that is something related with CO2 levels, but with the particle filter (at least on the diesel, don't know if you all have Diesel engines), very low revolutions on a cold engine generates higher level of particles on the exhaust gas circuit, forcing the engine to work harder, (more revs and no coasting) leads to a steeper increase on the temperature of the engine (oils and gases), activating the particle burning process in a short therm.
Of course this could be managed by the car computer. He knows that the car is cold and could work on specific regime until the car reaches the optimal temperature, and then, automatically go to the Drive Select chosen by the driver.
Sorry for my English, I hope you understand me