Comment 3 for bug 1737771

I can see why this happens - the private-address is only set when the -joined hook runs on the relation - https://github.com/openstack/charm-interface-bind-rndc/blob/master/requires.py#L30

As the -joined hook is not re-executed on charm upgrade, the revised data never gets set; removing and re-adding the relation would resolve the issue as described in the original bug report.