When you click on the TopCtrl, it brings up an OverlayTrigger...
When you submit the promote thread overlay trigger, it runs through and sends the data back via AJAX to prevent page reload. This is a problem with this however... in addition to the word "Promote Thread" on the TopCtrl, there is also a <span> tag.
return $this->responseRedirect( XenForo_ControllerResponse_Redirect::SUCCESS, XenForo_Link::buildPublicLink('threads', $thread), null, array('linkPhrase' => '<span>'.new XenForo_Phrase('promote_options').'</span>') );