ODM setting/unsetting fields

Here is the non-working code:

class User extends \Phalcon\Mvc\Collection
    public $login;
    public $email;
    public $password;

    public $confirmed = false;
    public $confirmationCode;

    public function confirm()
        $this->confirmed = true; // can be eliminated

Basic account entity, supposed to be confirmed via email. PHP unsetting as well as initializing fields some fields which weren't initialized(persisted) at first save and resaving doesn't work. Natively $set and $unset operators used in update. ODM equivalent for update is save. What is the workaround?

edited Mar '14

Nvm - Answer not relevant.

            update(array('_id' => $this->_id), array('$unset' => array('confirmationCode' => '')));