• If entering a world in VR, leaving VR does not allow any page turns. Only happens on 1.19.4 and below, despite the issue seemingly being in ImmersiveMC code. This is an issue in the older version of MC VR API that's used in development for 1.19.4 having a bug where switching out of dev mode doesn't actually result in the player as being recognized as out of VR.
• Looking at a lectern, leaving the world, then rejoining, causes the book to be blank. Confirmed on 1.19.4 and 1.20.4.
  • This happens due to the storage restoring itself before the book is set. With 0 available pages to the book, maxLeftPageIndex() returns -2 as the highest left page index. The storage should also store the book to make this restoration work, even though it isn't a source of truth.

In testing 1.18.2 at least, the page seemingly doesn't save, with neither save() nor load() being called. I consider this acceptable behavior, though I'm noting it here in case I do go back to investigate in the future.