It's normally caused by an accidental lifting of the brake pedal, usually when entering or exiting the car. Basically if the pedal is lifted, it depresses the plunger and thus resets the 'activation point' a bit further down. This means that when the pedal is at rest it may be on or above the activation point causing hyper sensitive brake lights, flickering lights or even lights that are permanently on in some cases.
Just need to be careful you don't lift the pedal is all.
