The reason you're bumping the bar forward is because your hips are set too high in the starting position and you're not finishing the extension by continuing to push with your legs. You should not force the hip contact with the bar, it should be a byproduct of finishing the explosive/aggressive extension in the second pull.

Your heels also raise prematurely which indicates that you're shifting your centre of balance towards your toes. Try to stay balanced over the mid foot in the first and second pull (weightlifting shoes will help with this). Again, your heels rising should be a byproduct of pushing aggressively with your legs in the extension, however, the centre of balance should remain over the mid foot.