The player is unable to attack through closed doors, some mobs can attack the player through closed doors, yet the player is unable to. Even though sometimes, parts of the mobs are showing on your side of the door, clicking attack will not hurt that mob.

Reproduce:
1. Build door.
2. Put mob on one side of the door, make sure it is showing on both sides.
3. Attack the mob on the other side of the door.
4. Note what happens. Unable to attack the mob.