If I change something in Connection settings (f.e. MTU, gateway) through NetworkManager applet and close dialog then error message popups and I lost all my changes.

Excerpt from error message: connection.gateway-ping-timeout: can not set property: value...

I attaching screenshot of message;

Snippet from .xsession-errors:

QXcbConnection: XCB error: 2 (BadValue), sequence: 12829, resource id: 106954756, major code: 142 (Unknown), minor code: 3
Currrent active notifications: QHash()
Guessing partOf as: 0
 New Notification:  "Nepavyko atnaujinti ryšio Namu-laidinis" "connection.gateway-ping-timeout: can not set property: value \"41457456\" of type 'guint' is invalid or out of range for property 'gateway-ping-timeout' of type 'guint'" -1 & Part of: 0
D-Bus call: "org.kde.Spectacle" : "/" : "StartAgent" : ()

I encounter this when installed Kubuntu 16.04 (freshly). This happens even in LiveCD session.

Reproducible: Always

Steps to Reproduce:
1. right click on Connection icon and choose "Configure connections...";
2. create or edit existing connection;
3. change something, f.e. fill inn fixed IP, DNS, gateway, or change MTU;
4. close dialog -> error message;
5. reopen last edited Connection -> all changes reverted to default