Not enough explanation, this literally says nothing what the "bug" is

When trying to fire an arrow at the player, the NPC will always fire even with a friendly in the way, this causes damage to the friendly NPC and the one firing the arrow will not stop.

ok, thank you, well technically it isnt a bug, but more something of the sort of "we didnt thought about xxx", will be fixed asap

Vanilla behavior, we'll see what we can do about it, but it's bound to happen by accident at some point.