Points never get subtracted. Technically, theoretically and practically it's impossible, at least. Furthermore, blows to certain joints deal more damage. Hitting the head scores much more than for example the triceps. If you indeed have a replay that proves otherwise, give it to us. This system has been waterproof till now, so I seriously doubt if there's a legitimate glitch here. If you hit the enemy with your knee or elbow or whatever, you're likely to get as much damage as you deal.