I use rockwell, no margins and a pretty small font size, and still routinely get widow/orphan problems. Most notably at the beginning of chapters where the chapter number appears on a page on its own and the text begins on the next page. This seems to happen even if I alter the css.
I recently finished feedbooks' epub of "The Cossacks", and this was full of empty chapter pages. (
http://www.feedbooks.com/book/1528/the-cossacks)