In most/¿all? epub files, every page is an html document, but we are putting everything into a single QTextDocument. This makes that stuff like the file at bug 206268 gets confused, it sets the background black for the first page only but it ends up affecting all the file.
Just to be clear: this is another bug coming from the sample document of bug 206268.
Thank you for the bug report. As this report hasn't seen any changes in 5 years or more, we ask if you can please confirm that the issue still persists. If this bug is no longer persisting or relevant please change the status to resolved.