public function updateMessageBlock(Varien_Event_Observer $observer)
    {
        $block = $observer->getBlock();
        if ($block instanceof Mage_Core_Block_Messages
            && !($block instanceof EcomDev_Varnish_Block_MessagesInterface)) {
            if (!$this->_getHelper()->isAllowedCurrentPage()) {
                return $this;
            }

            // Add missing core session messages to our message model
            Mage::getSingleton('ecomdev_varnish/message')->addMessages(
                $block->getMessages(), 'core/session'
            );
        }

        return $this;
    }