RSS/Atom output and HTML tag support
When looking at Spezial:Version it shows SMW 1.9 but somehow I got the feeling it is an older version of SMW 1.9.
The ensure you use the current master you should use git clone https://git.wikimedia.org/git/mediawiki/extensions/SemanticMediaWiki.git
You can verify that you have the latest by looking at includes/queryprinters/FeedResultPrinter.php line 281 which should only contain
return FeedItem::stripComment( implode( ',', $items ) ) . FeedItem::stripComment( $pageContent );
If you can confirm that this the SMW version you are using then MW might be the next path to look into.