I'll wager the overtaking flasher is disabled on US spec MINIs. While this signalling is common and accepted in Europe, somehow it is viewed as impolite on US roads.
Imagine a country in which a majority of the population has no clue about driving safely at speed. Now, imagine that population considering overtaking signals as impolite!
Fortunately, I live in Massachusetts. People here are still flummoxed by indicator signals!
Help me....
Theo