This exact issue bit me too. Mine was outright dangerous in certain conditions as on a slight incline uphill, starting the car off would engage the engine so suddenly it felt like you were getting rear-ended. Took it in and they told me that this was a mistake in the original program of the transmission... but that it was $275 to update the software. Naturally, as with you, no joy under the CPO. I paid up and the car is much better. But this really is one of my biggest disappointments with BMW. The software had a bug. They sold the car with a defect... and I have to pay to fix it??? Seriously.
I hope someone there is watching as this is just a terrible blemish on the brand to have customers paying to fix their mistakes. The idea that software is not covered because it is not mechanical is just stupid and arbitrary. Tell me how these transmissions work without the software??? Software is just as important and integral as a solenoid in a modern transmission. Defects in it no different either.