[Phalcon 1.3.4]try to update relation column fail

Hello , I use models like this

namespace Namespace;
class STable extends \Phalcon\Mvc\Model
{
    /**
     * @var integer
     */
    public $sid;

    public function initialize()
    {
        $this->hasMany("sid", "\Namespace\P", "Sid", array('alias' => 'pdatas'));
    }
}

namespace Namespace;
class PTable extends \Phalcon\Mvc\Model
{
    /**
     * @var integer
     */
    public $pid;

    /**
     * @var integer
     */
    public $Sid;

    public function initialize()
    {
        $this->belongsTo("Sid", "\Namespace\STable", "sid", array('alias' => 'sdata'));
    }
}

And I can create record use by save() successful , but when I want to update the $Sid it not working , still the same value before

The data below was I try to do:

//Created and fetch
array (size=13)
  'pId' => string '11' (length=2)
  'Sid' => string '136' (length=3)
  'paydate' => string '104/06/29' (length=9)
  ....

//Try to be ( but Sid still 136 )
array (size=13)
  'procurementId' => string '11' (length=2)
  'Sid' => string '128' (length=3)
  'paydate' => string '104/06/29' (length=9)
  ....

How can I do?