CLEANED UP POST, AS REQESTED BY Galaxy_2Alex

I noticed that the naturally generated blacksmith's building will cause villager deaths if a door is added. Remember, players often fix up villages by adding doors where they're missing and adding new buildings (which as far as I know was encouraged by Mojang). The reason for it causing villager death is based on how villagers see houses. They look for doors then check a line of 5 blocks on either side of the door for open sky. Whichever side of the door has more open sky counts as "outside". With the blacksmith building all 5 squares of the real outside are covered by the porch roof. And inside only 3 squares are covered (2 with roof above them, 1 from being a solid wall, then 2 sky blocks on the other side of the back wall). This causes villagers to mistake the front porch as the "inside" and attempt to hide from zombies out there. Needless to say it doesn't work too well. They are smart enough to scatter as the zombie gets close but they might not make it to another building before being cut down (if there's multiple zombies coming from multiple angles for example).

Now I'm not suggesting changing villager AI. Rather the location of the open doorway should be moved to where it borders the street (like every other house in the village). Most players will use wherever the doorway is as the spot to put the door rather than filling it in and picking their own spot after all.

Also as requested I'm including screenshots of an experiment to see if they do it independent of a village (in a blacksmith building in the middle of nowhere). The answer is yes, they do. One was already in the building during the day. Come nightfall the other 2 gathered on the porch, and after another 15 seconds the one inside came out onto the porch. When a zombie finally showed up they scattered once he got too close. As I said before, in a more cramped village situation with multiple zombies coming from multiple angles they are much more likely to be killed. I'm also including 2 screenshots illustrating the 5 blocks on either side with red and blue wool. Parts of the wall or floor are temporarily removed to allow you to see all 5 blocks of wool. Obviously the blocks are there during testing.

ORIGINAL POST:

Just fixing up a village and thinking about that 5 ceiling blocks in front of the door rule (that allows villagers to tell which side of the door is "inside") when it occured to me that a blacksmith with a door added would count the outside porch as "inside". This explains why I've seen villagers just hanging out on the porch at night. I thought they were just derps. I've even seen a zombie cut down a villager on that porch and didn't clue into what was really happening until now. This can be fixed by changing those blocks to stone slabs (provided they're not upside down slabs). While you're at it change that double-slab surface outside to an anvil (ok that 2nd one is a suggestion not a bug).