Zombies break down iron doors

Was making a secure bunker and noticed a zombie at my iron door. Started laughing because he was trying to break it down but that ended quickly when he actually did break it. I would like to see this fixed because you can't make any secure rooms without zombies breaking your door down anymore (unless, of course, you use pistons.)

How to reproduce:

Just put a villager/survival player in a room with an iron door and a zombie outside. Might take a couple of seconds for him to become interested and start breaking the door