I'm stuck, can someone please explain how an open at X would cause the passenger side to work in the UNLOCK position ONLY?
It's because there's only one ground. The passenger switch grounds through the driver side switch. With one leg open, you can only have ground in one direction. When you go Lock you have both power and ground. When you go in the other direction, you have power, but no ground.
Why make it simple, when it will work equally as well complicated.