The theme tries to show as HTML5, however the code doesn't pass validation:
Line 56, Column 110: Bad value EditURI for attribute rel on element link: Keyword edituri is not registered.
…cation/rsd+xml" title="RSD" href="http://www.dragonflame.org/xmlrpc.php?rsd" />
One way or another a theme should implement a standard. If the error is on WordPress side, then the theme should validate for a standard that WordPress core also supports, otherwise without manual intervention the site will never validate.
If the error is on theme side, then it should be fixed.
However, I suspect the error is on theme side, since I managed to fix it manually a while ago and it only came back after the latest theme update. Still, it's annoying to have to manually fix the theme after update.