I have recently installed Ubuntu 16.04 .and my networking settings are Proxy oriented. I added IPv4 settings and saved them but when I see the added IPv4 settings again, the subnetmask settings are not saved as I entered. In the place of subnetmask (255.255.252.0) a default number 22 is saved as show in the image below.
I don't know why that number has been appearing again and again even after saving required IPv4 settings.