Villagers can open Iron Doors

So, I created this villager farm where I have at least 40 villagers in one big house. In order for me to leave that house, I have to go through 2 iron doors (I made them iron so the villagers do not escape). However, once I open the door and walk away a block or two, a villager can easily open the door and walk out. They can't do it by themselves, so I was wondering if they're supposed to do that?