change mail domain client_id via API

Hello,

When I try to change the client_id for a e-maildomain via API, then the e-maildomain is changed to the new client_id.
This works.
But all mailboxes which belong to the e-maildomain are not transfered to the new client_id.
Is this as it should work? And do I need to change the client_id for mailboxes also?

Jim.

relevant code:
$mail_domain_record = $client->mail_domain_get_by_domain($session_id, $maildomain_name);
$maildomain_id = $mail_domain_record[0]['domain_id'];
$mailclientaangepast = $client->mail_domain_update($session_id, $ispc_new_client_id, $maildomain_id, $mail_domain_record[0]);