How are headshots ruining perfect hides?

The animal when alive shows a perfect hide... often, when I shoot them in the head, regardless of weapon, sometimes the hide goes down a star. I can't figure out why this is. Maybe the shot isn't actually as accurate as it looked when it was tagged, but I'm hoping the game doesn't expect only certain weapons will preserve perfect hides even when with a headshot... that seems silly. A headshot doesn't pierce the body of the hide.