i used to jump forward on all my lifts and two cues helped me, which may help you:
1. do not initiate the "jump" until the bar is as far past your knees as possible. I have found that the lower your back angle is when you start to jump, the more likely your toes, your knees, your hips, your whole body has the tendency to go forward, rather than up or back.
2. finish the extension violently. i think its the same concept, but if your "explosion" point is earlier in the lift when your back is at an angle, its likely to pull you forward. if your "explosion" point is more when your back is vertical or even inclined, its likely to push you straight or back.