Built a shelter in a mountain and had zombies coming to attack me. As I opened the door, the zombies (instead of attacking me directly) started going to the left side of the door and climbing up above. They ended up jumping off from above and attacked me that way.
Environment
PC
The actual problem is that zombies sometimes can't go through doors. They can't do it if they have CanBreakDoors:0 and the target isn't a villager. Confirmed in both 1.9.4 and 16w21b, with player, snow golem and a skeleton (the mobs provoked the zombie).
Steps to reproduce:
Build a room with a door (a place, which can be exited only through door(s))
Summon a zombie in it via
Make sure you are outside of the room, and a zombie (normally) can come to you.
Switch to survival mode.
Open the door.
The result: the zombie would be stuck behind the door.
Not sure if this ticket should be changed, or a new ticket should be made.