The com_content override uses a <span> tag for itemprop (as did J!3.3). Because the editors insert <p> and other tags that are invalid HTML inside <span></span> some browsers fail to render content and validators output lots of errors.
The Wanderers template still uses <span></span> for itemprop tags.
The discussion covers using <section> tags but the issue was resolved using <div> tags instead to be compatible with IE8 and other non-HTML5 browsers. I have tested this locally converting <span> to <div> on lines 196 & 198 of the file wanderers/html/com_content/article/default.php.
The related bug and issue is found here: