protected function _getSourceStore()
    {
        // this may return a Mage_Core_Model_Store or a Mage_Core_Model_Website
        $configSource = $this->_validatorHelper->getConfigSource($this->getRequest());
        // When given a website, get the default store for that website.
        // AMQP config is only at global and website level, so no *current*
        // possibility for the default store to have a different value than the website.
        if ($configSource instanceof Mage_Core_Model_Website) {
            return $configSource->getDefaultStore();
        }
        return $configSource;
    }