Since I first posted in this thread I bought a 2011 M56. Now I'm wearing the shoe and I know where it pinches... at least it did for a while.
For a US market car, my AUTO setting pretty much worked like the ON switch. Which means, even in bright sunlight, with the headlight switch in AUTO, the headlight still came on.
I checked the front and the HID was on full power, I played with the sensitivity settings and that didn't change much.
Tried the high beam and that came on too, turning off the fog light as expected. Again, which told me the lights on definitely weren't driving lights.
So I turned off the fog light, and BAM! Everything is back to normal.
I usually like to have those set to ON so that I get some low ground clearance whenever the headlights come on.
I haven't had a chance to go cover to cover on the M56 owners manual yet, but I hoped having owned enough Infinitis I'd be able to get the vehicle on and off the road safely... but I suppose having the fog light switch to ON is a sort of bypass of the dusk sensor and just behaves as if the headlight stalk has been turned on.
Happy motoring
