The jolt you feel is related to the preload torque in the gearbox when parked. Try this experiment. Park on a medium sloped hill. Stop the car, don't use the park brake, turn off the car, let it place the DCT in P automatically, restart the car and feel that jolt when you place the car back in gear. The preload simply makes the gears stick more, requiring more force from the actuators to move the selectors and syncros. Repeat the same thing but use the park brake firmly before shutting off the engine - you find way less jolt.