RSS/Atom output and HTML tag support
I'm guessing you are using SMW 126.96.36.199 while smw.org already uses SMW 1.9. Either you wait until 1.9 is officially released or you use the git master to get access to the updated FeedResultPrinter class.
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.
I just added a test case  that verifies that a text like "A&O Berlin" will output "A&O Berlin" for the current SMW 1.9 master.
Aside from the SMW version and not related to the above issue it seems you are using 1.19.2 where its commendable to at least use MW 1.19.7 as unit tests deployed with SMW 1.9 (current master) are tested against MW 1.19.7, 1.21, and 1.22.