Because arrows are literally bouncing off of me. I still take the full brunt of the blow, but if someone shoots me, there's a 50 percent chance it bounces off the ground and I can pick it up. A nice way to get some of the more expensive arrows, but peculiar nonetheless.
I have notice that when I tag a bandit or other mobs that the arrow will kill/hurt em but bounces back at me every once and a while and it's not happening to the ones wearing armor, it's happening to the ones in leather or fur, I could understand it if they were wearing iron/steal armor.
I've only noticed it when it made sense. i.e. a character (or myself) wearing heavy, high quality armor, blocking it with a shield, or (and this happened to me twice) my arrow hitting their weapon shaft.
Hmm, I must be sponge then, because I look like a Porcupine after most skirmishes with bow users. I have to open up a corpse and drop all the arrows that are shot at me.