Ok, thanks. This issue would be fixed in upcoming version. As quick solution you have to open /components/com_jcomments/jcomments.php and replace code:
$attribs = array('type' => 'application/rss+xml', 'title' => strip_tags($object_title));
with
$attribs = array('type' => 'application/rss+xml', 'title' => htmlspecialchars(strip_tags($object_title), ENT_COMPAT, 'UTF-8'));
and (for Joomla 1.0 users)
$html = '<link rel="alternate" type="application/rss+xml" title="' . strip_tags($object_title) . '" href="' . $link . '" />';
with
$html = '<link rel="alternate" type="application/rss+xml" title="' . htmlspecialchars(strip_tags($object_title)) . '" href="' . $link . '" />';