Can't assign Super+L to Lock Screen

[relgames]

Installed Ubuntu 12.04 64bit today, switched to Gnome Classic (no effects) and I can't assign Super+L to Lock Screen function.

I go to System Settings -> Keyboard -> Shortcuts -> System, then I click on Lock Screen and press "Super + L", it appears in the list but when I press it again it doesn't work.

If I set it back to Ctrl+Alt+L it works again. Actually, I tried to set it to different Super + ?? combinations, and neither of them work.
if I assign Super+L to so other command, like Start Terminal, it works.

1) The release of Ubuntu you are using, via 'lsb_release -rd' or System -> About Ubuntu
Description: Ubuntu 12.04 LTS
Release: 12.04

2) The version of the package you are using, via 'apt-cache policy pkgname' or by checking in Software Center
gnome-control-center:
  Installed: 1:3.4.2-0ubuntu0.3
  Candidate: 1:3.4.2-0ubuntu0.3
  Version table:
 *** 1:3.4.2-0ubuntu0.3 0
        500 http://nl.archive.ubuntu.com/ubuntu/ precise-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     1:3.4.1-0ubuntu1 0
        500 http://nl.archive.ubuntu.com/ubuntu/ precise/main amd64 Packages

3) What you expected to happen
Super+L locks screen

4) What happened instead
Nothing, I just see "L" typed in a text field (if focus is on a text field)

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: gnome-control-center 1:3.4.2-0ubuntu0.3
ProcVersionSignature: Ubuntu 3.2.0-27.43-generic 3.2.21
Uname: Linux 3.2.0-27-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu11
Architecture: amd64
Date: Mon Aug 6 10:14:36 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Release amd64 (20120425)
SourcePackage: gnome-control-center
UpgradeStatus: No upgrade log present (probably fresh install)
usr_lib_gnome-control-center:
 activity-log-manager-control-center 0.9.4-0ubuntu3
 deja-dup 22.0-0ubuntu2
 gnome-bluetooth 3.2.2-0ubuntu5
 indicator-datetime 0.3.94-0ubuntu2

[Sebastien Bacher (seb128)]

 Thank you for taking the time to report this bug and helping to make Ubuntu better. This particular bug has already been reported. Feel free to continue to report any other bugs you may find though

[relgames (relgames)]

Hello, please stop closing this issue without providing a link to already reported bug.
Thank you.