Affects Version/s: Minecraft 1.12
Fix Version/s: None
Windows 10; Java 1.8
Reproduction steps. In a single player world, obtain a new Book and Quill. Source does not matter, but the Book and Quill must be new. Take to an anvil and rename to anything different.
After you have retrieved the renamed Book and Quill, you are now unable to type into the book. You are able to still generate new pages and sign the book and quill.
Additional notes. Signing this renamed book without adding pages can generate an "Invalid book tag" exception (at least in multiplayer gameplay).
First observed in multiplayer, but this report is for non-modded single player (vanilla).
Suspect that this affects previous versions, but did not test.