I'm not entirely sure this is a bug, but I hope it is! I noticed that one of Willow's tiny downsides is that she becomes frozen faster, which includes ice staff in PVP! So, I think its weird that Bernie is unable to attack other players in PVP, but he can attack other mobs. I hope this is a bug because with Bernie Willow could be more interesting to play in PVP.
Attack another player in a PVP world while Bernie is active. Bernie will not attack the player.