Brakes are applied to stop wheels from spinning gradually, whether it is backwards or forwards. We have to visualize all states of movements as separate instances or snapshots. When a car moves forward, brakes try to decelerate and stop car moving forward. As soon as the car enters in the state of moving backwards, brakes will try to stop moving it backwards too, deceleration in other direction.
When the car is inat zero speed, brakes are not really needed, until unless another force (wind/engine/collision/manual) is trying to push it backwards or forwards.
