if you set IP V6 DNS servers they are properly stored, but they are displayed in IP V4 format when you reopen gnome-control-center network and validation fails

if you set IP V6 DNS servers they are properly stored, but they are displayed in IP V4 format when you reopen gnome-control-center network and validation fails.

Steps to reproduce this bug.
Open gnome-control-center network and go into IPV6 setting for wired connection.
Enable IPV6 with Automatic address.
Disable automatic DNS.
Enter google public IP V6 DNSes
2001:4860:4860::8888
2001:4860:4860::8844
Apply, and close gnome-control-center.

Reopen gnome-control-center network and go into IPV6 setting for wired connection
and you get this DNS servers with red color (failing validation) - see attached screenshot
32.1.72.96
32.1.72.96
and you can't apply setting until you change these wrong addresses.

ProblemType: Bug
DistroRelease: Ubuntu 16.10
Package: gnome-control-center 1:3.20.2-0ubuntu2
ProcVersionSignature: Ubuntu 4.8.0-30.32-generic 4.8.6
Uname: Linux 4.8.0-30-generic x86_64
ApportVersion: 2.20.3-0ubuntu8.2
Architecture: amd64
CurrentDesktop: GNOME
Date: Thu Dec 22 11:02:20 2016
ExecutablePath: /usr/bin/gnome-control-center
InstallationDate: Installed on 2016-12-16 (6 days ago)
InstallationMedia: Ubuntu-GNOME 16.10 "Yakkety Yak" - Release amd64 (20161012.1)
ProcEnviron:
 PATH=(custom, user)
 XDG_RUNTIME_DIR=<set>
 LANG=it_IT.UTF-8
 SHELL=/bin/bash
SourcePackage: gnome-control-center
UpgradeStatus: No upgrade log present (probably fresh install)