Your X5 should also be equipped with a Brake Override feature. This functions when there is a throttle input, and a brake input simultaneously that are in conflict. This usually requires for the throttle input to be recognized first, and then a brake input occuring after and together (to prevent against activation during a hill start with brake on, for example). In cases of a throttle/brake conflict, the brake should take precedence and kill the throttle signal. If the brake is pressed hard and quickly enough, the brake assist function may also kick in and cause the pedal to descend rapidly, and the abs to kick in causing brake pedal pulsation.