The UI Scale option when the game starts is "default". Clicking it once switches it to "medium" without changing anything, further clicks have no effect. Tested on both a custom book and a default test book.

I was running code from ec82535, but it had the same problem with the maven jar 1.0-7.9.
Run in Eclipse under Ubuntu.

I can replicate this when opening the game with a small screen, as is launched by default from a dev environment. It's not a problem with larger screens; but it does disable the ability to go back to a smaller size.

Apparently at such small screen size there is also only the medium option. This has been changed so that if there is no option, the resize button isn't shown either. Also, if the largest option has been reached, the button will now go back to default size instead of medium.