I found the two files, proposed.list and proposed.list.save in /etc/apt/sources.list.d folder and both of them had the same content:-
deb http://gb.archive.ubuntu.com/ubuntu/ xenial-proposed universe main multiverse restricted Neither file had that one line commented out with a # as I would expect. I removed those files and now I can enable and disable the proposed repos and if enabled the /etc/apt/sources.list file contains a line as shown above as I expected. -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1592427 Title: I can't disable proposed updates To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/software-properties/+bug/1592427/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs