Quote Originally Posted by MajinSaha View Post
..There is no typo, as well as no "disk", "sudo" and "dip".
Please try adding yourself to these groups -
sudo adduser saha sudo
sudo adduser saha dip
sudo adduser saha disk
Then reboot and see if you can use the MAC id in the new connections you create. I'm guessing that you are not able to use a MAC address (thus preventing 'you' to use a local network device) because of not being in 'dip' user group. You are able to use automatically created connections because those are created by system services automatically (hence by 'root') and are configured to 'Allow Everyone' to use them.

Anyway, this is just a guess and I'm not sure if that is going to make any change. But can you try a Live CD/USB to see if the interface gets a HWaddr automatically there? Or if you can save the MAC addresses newly created 'Demo' connections in the Live sesssion? If yes, I recommend doing a fresh install unless you are willing to try various cumbersome 'patches' to do something as simple as spoofing an address, which should be very easy on a healthy installation.