Car rolling forward in reverse?

Twice I have been parked on a slope and tried to reverse in my 2006 Honda Civic lx and it rolls forward slowly. Each time i hit the brakes but for some reason they don't work when doing this. I try hitting the gas to make it reverse and counter the fall but it doesn't work. I had to pull the handbrake or I would have hit the other car. via /r/cars http://ift.tt/2tY7QS4