I ended up making the booking I posted above. I tried on the website, but it gave an error and ended up making me a Points Advance reservation even though I had enough points. I cancelled that one and went back to the app with the weird cash prices. Just as before, these dropped off on the booking page, and everything looks normal on my confirmation email. For a split second, you can see the booking page refresh and take a cash number off. This is obviously some sort of odd app logic glitch.