Now some people on Autosport forums suggest that LH hitted the button that switches the pitlane speed limiter on and off and that is why the car suddenly slowed down. Look at the video before the FOM takes it down:

http://www.youtube.com/watch?v=MqHZ_xaB4Es

McLaren's steering wheel, button n*2:

http://www.mclaren.com/features/technical/interactive_steering_wheel.php