Fitment of BMW's first double-clutch gearbox (like Volkswagen's DSG, Nissan's GT-R tranny, and the SST in Mitsubishi's Evo X) went slightly wrong for at least 2,500 M3s, NHTSA concludes. "In a situation of rapid vehicle deceleration, the transmission software may perform a multistage downshift." Unanticipated stalling may occur; and that's dangerous.
Updated software is the answer, unsurprisingly. BMW dealers will reprogram the engine and transmission control units. The M3s involved are from the 2008 and 2009 model year, and you surely know if you've not been rowing your own gears lately. Been having problems with downshifts, oh ye M3 owners? Your problem will soon be solved.