The recently added "game randomly adds doors to nearest village" mechanic (Mojang's attempt to grief iron golem spawners) could trigger the "adding a door to the blacksmith kills villagers" bug (the villagers see the wrong side of the door as "inside" due to the placement of the doorway and so get picked off by zombies at night). I've been unable to get the mods on this site to count that blacksmith thing as a bug (since a door would need to be manually added and they CLAIM mojang doesn't intend players to add to the village), but since this new mechanic in 1.8 causes the game to add the door it's now something that happens without player interference.
EDIT: Just to be clear the solution is to move the doorway so it's facing the street like every other village house. I'm not suggesting that the villager AI needs changing. It's the building that's the problem, and even then it's just where the doorway is that's the problem.
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Not a duplicate, in the sense that the newly added behavior of the game adding doors to the nearest village now means that the game can do it on it's own without a player adding anything.
The game doesn't actually place new doors randomly. What that change means is that doors that are placed by the player close to the village are counted as part of the village.
While it's true that Mojang intends for players to be able to expand villages, that doesn't mean players don't have to be aware of the rules for what counts as a house. If they add a door in a position that will cause the game to consider a structure a house, but they leave an opening for monsters to get in, then that's on the player.
Duplicate of MC-51196