Другой простой способ получить / установить реферер - добавить параметр в ваш frontController в вашем коде начальной загрузки:
$frontController = Zend_Controller_Front::getInstance();
$frontController->setParam('referer', $_SERVER['HTTP_REFERER']);
и затем захватите реферер с вашего контроллера следующим образом:
$referer = $this->getInvokeArg('referer');
Из документов Zend для Zend_Controller_Front:
7.3.4. Front Controller Parameters
In the introduction, we indicated that the front controller also acts as a registry for the various controller components. It does so through a family of "param" methods. These methods allow you to register arbitrary data – objects and variables – with the front controller to be retrieved at any time in the dispatch chain. These values are passed on to the router, dispatcher, and action controllers.