Why did a "Chapter 3: ..." line appear inside the text of a chapter in the editor?

The AI does not always start a chapter the same way: sometimes with the title as a heading, sometimes with a plain "Chapter 3: ..." line, sometimes with the title twice, sometimes with no title at all. BookyAI keeps the chapter's real title in the book's details, shows it above the text in the editor, and removes such lines when it exports, so the exported book was always right. From version 1.9.23, every chapter the AI writes or rewrites is saved with the book's own title on top and no repeated "Chapter N" line. A chapter written before keeps its old opening until it is regenerated; you can also delete the extra line in the editor.