Zombies Don't attack sleeping villagers when broke in

This is an interesting bug.
How did i found this bug
Well while playing hard since it was hardmode the zombie were chasing me and then i found a village and i found a zombie that gonna break the door and then a spider came to me to kill me and a creeper almost killed me while the zombie is breaking the door at a villager's house and a spider attacked me again. and when the zombie broke the door i was shocked why does the zombie doesn't kill the villager it's like he just looking at a villager sleeping and i attacked it it didn't attacked me and even the zombie child, is this a bug or what