$this->session->set_flashdata('purchase', array());

function purchase() {
  $this->session->keep_flashdata('purchase');
  $data['item'] = $this->session->flashdata('purchase');
  $data['result'] = $this->store_model->get_cart($data['item']);

  $this->load->library('form_validation');
  if ($this->form_validation->run() == false) 
  {
    // views - 주문서작성폼
  }
  else
  {
    //DB입력
    $data['post'] = $this->input->post();
    $thankyou['traceno'] = $this->store_model->order_insert($data);
    if ($thankyou['traceno'])
    {
      //장바구니삭제
      $this->store_model->cart_delete($data['item']); //여기서 $data['item'] 이 사라집니다!
      //기타처리...
    }
  }
}

$this->form_validation->run() 부분에 keep_flashdata 를 넣어봤는데도 안되고요...
뭐가... 잘못됐나요? 세션설정은 다음과 같습니다.

$config['sess_cookie_name']        = 'session';
$config['sess_expiration']        = 7200;
$config['sess_expire_on_close']    = TRUE;
$config['sess_encrypt_cookie']    = TRUE;
$config['sess_use_database']    = TRUE;
$config['sess_table_name']        = 'cisessions';
$config['sess_match_ip']        = FALSE;
$config['sess_match_useragent']    = FALSE;
$config['sess_time_to_update']    = 300;