Warden in a roar loop when targeted mob dies

When a Warden hears a mob, then it starts to roar and target it. When the opponent dies the Warden is stuck in a roar loop forever until it hears another mob. I tested this out with a Creeper, when the Warden started to roar on it, then I lighted the Creeper and it blew up. After that the Warden got stuck in a roar loop.