Kill mobs through door (nexus 4)

So I was looking around my world and I found a village so I went to a building with a villager at the door and with my sword in hand when I clicked the door the villager got hurt and I was confused so I tried again and killed him I got curious to if a bug or not so a placed some cows in a hut and tried again and sure enough killed them (picture shows) (nexus 4)