Cannot set keyboard shortcut for "Lock Screen"

[Paul Natsuo Kishimoto]

To reproduce:
1. Cog icon → System Settings… → Keyboard → "Shortcuts" tab.
2. Select "System" in left pane.
3. Double-click beside "Lock screen" in right pane.
4. Press Scroll Lock.
5. Exit gnome-control-center (Alt+F4)
6. Press Scroll Lock.

Expected:
The screen is locked.

Observed:
Nothing happens.

$ lsb_release -rd && apt-cache policy gnome-control-center
Description: Ubuntu 11.10
Release: 11.10
gnome-control-center:
  Installed: 1:3.2.1-0ubuntu1
  Candidate: 1:3.2.1-0ubuntu1
  Version table:
 *** 1:3.2.1-0ubuntu1 0
        500 http://mirrors.mit.edu/ubuntu/ oneiric-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:3.2.0-0ubuntu6 0
        500 http://mirrors.mit.edu/ubuntu/ oneiric/main amd64 Packages

[Sebastien Bacher (seb128)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. The issue you are reporting is an upstream one and it would be nice if somebody having it could send the bug to the developers of the software by following the instructions at https://wiki.ubuntu.com/Bugs/Upstream/GNOME. If you have done so, please tell us the number of the upstream bug (or the link), so we can add a bugwatch that will inform us about its status. Thanks in advance.

[TomasHnyk (sup)]

Don't you have ubuntu tweak installed? If so, don't you have set under Tweaks > Session indicator "Disable lock screen?" If unsetting it corrects your problem, could you set this to invalid? Otherwise, set it to confirmed.

[Michel Bouckaert (mbouckaert-ign)]

Additional information (confirming the symptoms reported by original post):

If in steps (4) and (6) one enters the combination <Alt><ScrollLock> (or any of many such combinations), the effect is as expected, screen lock is activated.

However, for several single-keys, including ScrollLock, the problem exists as reported.

This is new to Oneiric. The problem did not exist in previous versions.

Regarding "ubuntu tweak". Synaptic / Software Center do not mention such a tool, and the Gnome-tweak-tool does not have any option like "Session Indicator"... Could you help identifying the tool you hinted at ?

[Paul Natsuo Kishimoto (khaeru)]

I don't see why it should be necessary to install a new package from a PPA to address this regression in basic functionality.

[TomasHnyk (sup)]

Seems it is a duplicate of bug 857623 - (and https://bugzilla.gnome.org/show_bug.cgi?id=660566 ) then. If you disagree, please unduplicate.