It's not a bug since the bullets come from your weapon and not from the center of your screen like in other games. In fact, if you pay close attention, the crosshair isn't even perfectly centered, meaning the bullets travel from the weapon to the center of the crosshair. And what does this mean? If you shoot point-blank, even if you're aiming at the center of the head, most of your shots will hit the chest. How do you fix this? Simply aim a few centimeters to the right, and you'll be hitting headshots. For the same reason, you can't shoot very, very close from behind cover