The bind-dyndb-ldap plug-in didn't handle DNS zones without 'idnsUpdatePolicy' attribute properly.
Harmless, but misleading error message "zone serial (<zone serial>) unchanged. zone may fail to transfer to slaves." was logged after each zone reload or potentially after each change in the affected DNS zone.
The bind-dyndb-ldap plug-in was fixed to not print any error message if 'idnsUpdatePolicy' attribute is not defined in the DNS zone.
DNS zones without 'idnsUpdatePolicy' attribute are processed correctly and no error message is logged.