Thanks for the bug report but this is not a bug. The login screen always exists separately on VT1 (Ctrl+Alt+F1) to your desktop on VT2 (Ctrl+Alt+F2). And the desktop is not meant to lock immediately. It should do after some period of time, but won't "if you were listening a web radio on Firefox" because that's a normal means of preventing the screen from locking.
** Changed in: gnome-shell (Ubuntu) Status: New => Invalid -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1936718 Title: screen doesn't automatically lock when switching to a virtual terminal To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1936718/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs