Stopped on a steep downhill (about 12%) for (perhaps) 20 seconds and as I went to pull away gearbox was in neutral - rolled forward and re accelerated and gearbox behaved as normal i.e. select correct gear. Any one else had this or is it a "characteristic"

A vsearch found some posts on "auto box downhill" where the same behavior has been seen. It is suggested that a software update was a possible fix but only one reply commented on this. So did the other posters update their auto box software or have they just accepted the behavior ?. As my car is out of warranty what is the approx cost of a software update and does it have to be carried out by a main dealer or can I use an independent ?.
Thanks for any comments