I have made "secret doors" with sticky pistons and levers. Mobs spawn freely inside the castle.
I was outside, attempted to pull the lever to get inside. It wouldn't open. I thought, enderman broke it. I find another way in, and go to inspect the internal lever. Lo and behold, a chainmail dressed zombie is standing up in front of the lever. I chase him off, and suddenly, when the zombie is no longer in front of the lever, the door works again.
I thought zombies couldn't affect stuff like that. Is this a new update maybe?