Ok, so I rang the garage, and the person on the service desk was not particularly helpful, but after a bit of discussion in the background came back with "the battery management module was updated"
To me that doesn't sound like anything that hasn't been done before, but they weren't particularly forthcoming ?
We've got another annoying fault now, where the main display is blank when the car is started, and doesn't respond to anything, and locking/unlocking the car doesn't sort it. It does come back to life of its own accord, and I've not seen this happen so haven't had chance to look at it. I'm not sure if it's a known issue, or something just affecting this car.