The UCR variable samba4/join/dnsupdate and the local mode for samba_dnsupdate are no longer necessary and can be removed. See Bug #27395 and Bug #28754.
This issue has been filed against UCS 3.0. UCS 3.0 is out of maintenance and many UCS components have vastly changed in later releases. Thus, this issue is now being closed. If this issue still occurs in newer UCS versions, please reopen.