That one specifically had a huge problem (which I'm realizing I'm saying from a story my driver's ed teacher told, I have not verified this, so take it with a grain of salt). Like you said, the lap belt was a separate step, but as I heard it, a lot of people didn't bother with that one because hey, automatic seat belt! Then you get in a crash and now your lower body is not restrained and you end up hanging yourself/breaking your neck on the shoulder belt as your body tries to submarine under it.
Similarly, the ones where the belts were connected to the door. That seems fine right up until you end up in a crash that causes the door to open.