ORM -storing related records

I am experiencing a strange behavior on v 1.3.4 :

class UserProfile
{
    // .... code
    public function initialize()
    {
        $this->hasOne('user_profile_user_id', 'App\Core\Models\User', 'id', array(
            'alias' => 'user',
            'reusable' => true
        ));
    }   
    // ... code
}

class User
{
    // .... code
    public function initialize()
    {
        $this->hasOne('user_profile_id', 'App\Core\Models\UserProfile', 'id', array(
            'alias' => 'profile',
            'reusable' => true
        ));
    }   
    // ... code
}

Creating a record :

        $security = $this->getDI()->get('security');

        $user = new User();
        $user->setUserFirstName($data['user_first_name']);
        $user->setUserLastName($data['user_last_name']);
        $user->setUserEmail($data['user_email']);
        $user->setUserPassword($security->hash($data['user_password']));
        $user->setUserIsActive($data['user_is_active']);

        $user_group_id = $this->findFirstGroupByName($user_group_name)->getId();
        $user->setUserGroupId($user_group_id);

        $profile = new UserProfile();
        $profile->setUserProfileLocation($data['user_profile_location']);
        $profile->setUserProfileBirthday($data['user_profile_birthday']);

        $user->profile = $profile;

        $user->create();

Will return me: user_profile_user_id is required

Anyone had similar problems ?