Closely relates to MC-262924.

The bug

The chiseled bookshelf's item model is defined via the file "chiseled_bookshelf_inventory.json" in the models/block directory, which is then used as a parent model by "chiseled_bookshelf.json" in the models/item directory. This setup is entirely redundant: the exact same result could be achieved by deleting the existing chiseled_bookshelf.json from the models/item directory, moving chiseled_bookshelf_inventory.json into the models/item directory, and then renaming it to chiseled_bookshelf.json, getting an identical result with one less file.