CI 3 + HMVC form_validation library problem

I have this couple of rules

PHP Code:

$this->form_validation->set_rules('password', 'New Password', 'callback__check_password');
$this->form_validation->set_rules('confirm_password', 'Confirm new password', 'matches[password]');

...

public function _check_password($password) {
    $result = empty($password) || (strlen($password) >= 10);

    if ($result === FALSE) {
        $this->form_validation->set_message('_check_password', 'MESSAGE ERROR');
    }

    return $result;
} 


and I receive this message on form submit: 'Unable to access an error message corresponding to your field name New Password.'
Even if I use a callback like this

PHP Code:

public function _check_password($password) {
    $this->form_validation->set_message('_check_password', 'MESSAGE ERROR');

    return TRUE // or FALSE;
} 


I get same error.