function no_submit_button_pressed(){
        static $nosubmit = null; // one check is enough
        if (!is_null($nosubmit)){
            return $nosubmit;
        }
        $mform =& $this->_form;
        $nosubmit = false;
        if (!$this->is_submitted()){
            return false;
        }
        foreach ($mform->_noSubmitButtons as $nosubmitbutton){
            if (optional_param($nosubmitbutton, 0, PARAM_RAW)){
                $nosubmit = true;
                break;
            }
        }
        return $nosubmit;
    }