But I didn't click on the Generate cover button, even though I have the plugin installed. I converted the files to epub, and when I opened the epub, it showed me that cover. Look:
I did not apply cover after importing the original file to the library.
Also, I just checked the original file: there's absolutely no paragraph styles. Just <p>Some text</p> and that's it.
I just sent that one particular book to disk, and when I open the epub in the internal vievwer, it still showed me the same cover.
A question: if I chose Send only EPUB to disk, why is there an opf file with it? What is its purpose? Can I delete it if I don't want it on my reader?