What can be done about the lawnmower jumping forward when you take your foot off the brake?

Try and release the brake at a slower rate.
Try and adjust the rpms to a lower rate.
Start in a lower gear.

Any mower will "JUMP" if you "POP" the clutch / brake. Try the suggestions above , and if you still have problems i would check that my pulleys underneath the frame, and above the mower deck, is moving when the pedal is depressed and released. You will need someone to help you with this task.

I Lost The Reply Question You Had Before I Could Answer It. Did You Solve Your Problem? Please Let Me Know If I Can Help You More.