Peter,
the issue you describe is a "school boy" error!
I was taught at school that NOTHING goes between an electronic component and ground/earth. All switches, controls and other stuff must go on the live side of a component.
Why? Because if the switch is on the wrong side then the component is never properly off and there is a risk of both overheating and electric shock. Also, as you describe, a motor is also a generator and back emf can do all sorts of strange things.
OK, on a car electric shock isn't a serious issue, but even so...
Yes, re-wire it.
PS: on the +8 the electrics/electronics are mostly BMW. I hope/suspect they do it correctly.
Peter
