In application/models/notifier/Notifier.class.php file in 125 row:
"subject" => $subject = lang("$notification notification $type", $name, $uid, $typename, $ws),
but before:
$css = get_workspace_css_properties($w->getColor());
$ws .= "<span style=\"$css\">" . $w->getPath() . "</span>";
After this in "$ws" we have html tags, it is ok for "$properties['workspace'] = $ws;", but not for subjects!
Simple solution:
"subject" => $subject = lang("$notification notification $type", $name, $uid, $typename, html_to_text($ws)),