since null == null and null == false and null == 0 but null === null and null !== false and null !== 0

the Zend_Rest_Server::returnResponse() function should be changed form

    public function returnResponse($flag = null)
    {
        if (null == $flag) { //<-- 2 equal signs
            return $this->_returnResponse;
        }

        $this->_returnResponse = ($flag) ? true : false;
        return $this;
    }

to

    public function returnResponse($flag = null)
    {
        if (null === $flag) { //<-- 3 equal signs or use is_null()
            return $this->_returnResponse;
        }

        $this->_returnResponse = ($flag) ? true : false;
        return $this;
    }

The way it is now, if you try to set it to false, it thinks it's null and returns $this->_returnResponse instead of setting it.