Passive mob movement is biased towards fence gates

The bug

Passive mobs like to go towards fence gates. You see, they seek freedom from their pens, and think that a closed fence gate is an exit, when really, it's not. Their pathfinding tells them that they want to go somewhere out side their pen, but there's a fence in the way. So what do they do? Go towards their fence gate, and then stop there because it's closed.