Trapdoors can stay on the wrong side of slabs

I am able to get trapdoors on the top half of a block of a half slab, since the hitbox of the slab doesn't allow placement this can be achieved by pushing the trapdoor with pistons. And similarly I am also able to get trapdoors on the bottom half of a block of a upside down half slab.
This make the trapdoor float in the air when closed.