When a wooden trapdoor is opened, the model appears to open on the opposite side of where it is actually attached. The hitbox is still in the right place, it just appears incorrect.
As you can see in the first screenshot, the trapdoor is supposed to be facing east but appears to face west. It should be attached to the spruce slab, but appears to be attached to nothing. The second screenshot shows the player standing on the hitbox of the trapdoor while there appears to be nothing supporting him.