From one of the sides of both wooden and iron doors, the textures is inverted, so it looks like the hinges are being moved and the grip is holding the door in place.
Just place a door of some sort and try to open it from different angles a few times. The textures should be flipped on the side of the door with the most space in between the next block and the door. Just make shure you see the door from different perspectives so you notice the "bug" (more like texture glitch, but whatever), because the door is only flipped on one side, while on the other side, it looks normal.
Thanks for taking your time!