I found this on a realm. To replicate this bug get a book and quill. Open it and type something. After this wait until you get kicked for AFK after this when you join back on the realm the text will be gone.
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This is expected behavior. The text in a book and quill is not uploaded to the server until you close out of the book. That produces the event that changes the book to contain whatever text you entered. Its painful but its how multiplayer works.