Zombies not attacking doors all the time

Quite simply, zombies are not attacking doors, they are not banging on doors, they do not break them down. I have observed this in my smp survival world. The difficulty is on hard. Zombies just stand outside the door moaning and looking inside, like how they did prior to the zombie siege AI update. This effects both the wooden doors pre-generated in villages and strongholds, as well as player created doors. The zombies don't smash the doors at all, villagers or players on the other side are safe.

• Okay so just now, 1 zombie attacked the door. It was the first zombie to do this, I've seen at least a dozen other zombies just stand there, look at me, then walk away. Posted some screens of the one who attacked and other who did nothing