Update OpenLDAP userPassword

[stegger]

I am trying to update a users password on OpenLDAP:

$new["userPassword"] = '{md5}' . base64_encode(pack('H*',
md5($newpass_in_plaintext)));
$this->result = ldap_modify($connection,
"uid=testuser,cn=users,dc=test,dc=net", $new);

I am authenticated and the operation succeeds (no errors), but the
password does not change.
How can I properly change a userPassword value in OpenLDAP?
Thank you for any suggestions.

--
Stefan