I'm not so sure this is due to battery overvoltage - your battery/regulator circuit would have been cooked by now if this is the case. It sounds like your battery has a cranking depletion which drops the battery voltage a lot when you start the car - if the battery has a high internal resistance, then it causes a big voltage drop at the battery terminals when a high current is being drawn. You even explain in your post that the thing works OK after the car is started, when the charing system has kicked in.

I think you might have a dead cell in your car battery, or one that is getting sick. What is the temperature in your part of the world? If it's as cold as it is here in NL at the moment, then this one possibility. Low temperature has a similar effect on a battery as high internal resistance. I had the same experience on a sickly battery in my Mini prior to version B6 (I think) where the power fail interupt was going active and effectively doing it's job properly, but at the wrong time...

With a new battery and the later software, it has not repeated.