The bug
When I copy & paste a text from anywhere (notepad, webpage, word, etc...) from windows into a book and quill, a carriage return control character is added at the end of each line.
I suppose it's because the new line char on Windows is "\r\n" (CR-LF), the CR char is displayed but it should not.
It's possible to avoid this problem using an advanced Text Editor that allow to choose the new-line char, using the linux mode (\n) there are no problem. Using the Mac mode (\r only), there are not new line, all text is collapsed with the CR char as separator. (See screenshots)
I had the same issue as well. I was creating an Adventure Map, and when I copied the text from my web browser, it started doing this.