skipAttributesOnUpdate seems not to work in Models

I have a model "User" that I want to validate the email-address of a user on create, but not on update.

<?php
use \Phalcon\Mvc\Model\Validator\Email,
    \Phalcon\Mvc\Model\Validator\Uniqueness;

class User extends \Phalcon\Mvc\Model {
    public $id;
    public $email;

    public function validation()
    {
        $this->validate(new Email(array(
            "field"    => "email",
            "required" => true,
        )));

        $this->validate(new Uniqueness(array(
        "field"    => "email",
        'message' => _('A user already exists for this email address')
        )));
    }

    public function initialize()
    {
        $this->skipAttributesOnUpdate(array('email'));
        parent::initialize();
    }

}

I have tried replacing $this->skipAttributesOnUpdate() with $this->skipAttributes(), with no luck.

I ended up with adding if(!isset($this->id)) in the validation method, is this correct? Phalcon v. 2.0.3