I have the same problem. You can't have the brake on to initiate launch control. And the car will not roll forward until you floor it...at which point I still haven't released the lever.
I don't get how you can use this usefully if it rolls forward when you don't want to.
It's like the engine revving is slowly engaging the clutch pushing the car forward. Weak!
09 Space Gray E90 M3 DCT: BPM (Stage 1, DCT and Servotronic) tune, Gintani Sport Exhaust, Dinan Intake