Typically this is a result of a parasitic draw and could be related to something internal in the vehicle but not often. We have seen this several times before and it turns out to be an accessory plugged into a power port (cigarette lighter, etc).
I don't know how many times we've seen it:
GPS Plugged in
Satellite Radio adapter plugged in
Phone or car charger plugged in
Sometimes they are left on, thinking the car will shut off power to them automatically, but this isn't always the case. I'm not sure if its part of the software that if there is a consistent power draw that the car will continue to provide power, but it will. Interestingly, these things are always "on" but will continue to have a parasitic power draw that the MINI or BMW will continue to feed.
The only other time I've seen this happen was when a customer smashed their light switch in and it was stuck in an interior light "on" mode, every other time it has been an accessory or device.