Model uniqueness validation triggered after successful insert

I have a problem, my model uniquenss validation is triggered after a succesfull update so I get both the success flash message and error flash message. I use slightly modified code from vokuro and invo examples.

//MODEL

public function validation()
{
    $validator = new Validation();

    $validator->add('email', new Uniqueness([
        "message" => "The email is already registered"
    ]));

    $validator->add("username", new Uniqueness([
        "message" => "The username is taken, try a new one"
    ]));

    return $this->validate($validator);
}

/**
 * Initialize method for model.
 */
public function initialize()
{
    $this->setSource("users");
    $this->belongsTo('role_id', 'Models\Role', 'id', ['alias' => 'Role']);
}

//CONTROLLER    

/**
 * @Route("/register", methods={"GET", "POST"})
 */
public function registerAction()
{
    $form = new RegisterForm();

    if ($this->request->isPost()) {

        if ($form->isValid($this->request->getPost()) != false) {

            $user = new User([
                'name' => $this->request->getPost('name', 'striptags'),
                'email' => $this->request->getPost('email'),
                'password' => $this->security->hash($this->request->getPost('password')),
                'hash' => $this->security->getRandomBytes(),
                'role_id' => 5
            ]);

            $this->flash->setAutomaticHtml(true);

            if ($user->save()) {

                $this->flash->success('You have successfully registered');

                return $this->dispatcher->forward([
                    'controller' => 'auth',
                    'action' => 'register'
                ]);

            }

            $this->flash->error($user->getMessages());
        }
    }

    $this->view->form = $form;
}

//VIEW
    {{ form("class": "form-search") }}

  <div class="page-header">
      <h2>
          Sign Up
      </h2>
      </div>

    {{ content() }}
    {{ form.messages() }}

    <label>{{ form.label("name") }}</label>
    <div class="form-group {{ form.hasMessagesFor('name') ? 'has-error' : '' }}">
        {{ form.render("name") }}
    </div>

    <label>{{ form.label("username") }}</label>
    <div class="form-group {{ form.hasMessagesFor('username') ? 'has-error' : '' }}">
    <div class="input-group">
        <span class="input-group-addon"><i class="fa fa-user"></i></span>
        {{ form.render("username") }}
    </div>
    </div>

  <label>{{ form.label("email") }}</label>
  <div class="form-group {{ form.hasMessagesFor('email') ? 'has-error' : '' }}">
      <div class="input-group">
          <span class="input-group-addon">@</span>
          {{ form.render("email") }}
      </div>
  </div>

  <label>{{ form.label("password") }}</label>
  <div class="form-group {{ form.hasMessagesFor('password') ? 'has-error' : '' }}">
      {{ form.render("password") }}
  </div>

  <label>{{ form.label("confirmPassword") }}</label>
  <div class="form-group {{ form.hasMessagesFor('confirmPassword') ? 'has-error' : '' }}">
      {{ form.render("confirmPassword") }}
  </div>

  <label>
      {{ form.render("terms") }} {{ form.label("terms") }}
  </label>

  <div class="form-group">
      {{ form.render("Sign Up") }}
  </div>

  {{ form.render("csrf", ["value": security.getToken()]) }}
  {{ form.messageFor("csrf") }}

  <hr>

  {{ endForm() }}