Solving FPS Walker 'bunny hop' effect.

I've had a look around and can't find a solution to the effecting I'm getting with the FPS Walker 'bunny hopping' when looking straight up? I've played around with the character controller origin and tried the enhanced fps script to no avail. If anyone has has a solution to this very distracting issue I'd greatly appreciate it.

Thanks.

After this line:

moveDirection = transform.TransformDirection(moveDirection);

Add:

moveDirection.y = 0;

I think that should fix it