Following situation:

Table 1 (contact_table):
contact_id (primary), tbl1_name, tbl1_address

Table_2 (additional_info_table):
additional_id (primary), additional_contact_id (relation), additional_content

Let's assume I have a contact table which is loaded always (Table 1).
I want to read, if there's an entry available from an additional table (Table 2). Table 2 always references to Table 1.

class myModel extends \atk4\data\Model {
    use \atk4\core\TrackableTrait;
    use \atk4\core\AppScopeTrait;

    public $table = "contact_table";
    public $id_field = "contact_id";
    
    function init(): void {
        parent::init();

        $this->leftJoin($this->'additional_info_table', [
          'master_field' => 'contact_id',
          'foreign_field' => 'additional_contact_id',
          'reverse' => true
        ]);
    }
}

When using this model in a form, it reads properly, but it just saves data from the main table. The data of the joined table is neither inserted nor updated.
Is this how it's intended to work? If yes, then how to deal with a situation like this?