Shot arrows sometimes bounce off of a mob or go right trought a mob without hitting it.
that most times does happen when trying to shoot many arrows fast in a row with a bow, not it a way where the arrows just go 1 meter but realy fly a good distance. 
but it happens sometimes too when shooting slow.

I dont know if i can attach a screenshot later but if i can i will , it is not easy to replicate this bug cose it is very inconsistent in it behavior.