Widows and Orphans should prevent that single lines will be on one page or another. In ePub it usually means that that if one line of the paragraph is on the next page, more lines are moved to the next page. There was a thread about that not long ago.
Your problem could be the result of the <br /> inside the same paragraph. If you want a line to appear before the paragraph or after the header, why not solve it with margins? Add a margin-bottom to the <h1> style in CSS or a margin-top to the <p>, perhaps even creating a special class for it, like this: