Reset of system shortcuts after reboot (switching workspace for example)

The following description references Ubuntu 12.10 and gnome-control-center 1:3.4.2-0ubuntu19.1

If I change the default shortcuts of "Navigation"->"Switch to workspace ..." (Alt+Super+Left for example) than the new shortcuts went right. After a reboot (next day) the default shortcut came back and is also displayed in "gnome-control-center keyboard"->"Shortcuts"

By the way, in Ubuntu 12.04 with Unity and 12.10 with Unity I am unable to assign Super+Letter combinations:
If I try to set a shortcut like Super+Left for switching Workspace or Super+E to open "Personal Folder" and the focus is on a text input field it types the letter "e" but the shortcut does nothing else. I know the Super-Key has special functionality in Unity, but Unity only uses the Long-Press, Super+Numbers, Super+s and Super+t. Why am I unable to assign the other combinations of Super+Letter?
I think it's the same problem like in Bug #1033439.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: gnome-control-center 1:3.4.2-0ubuntu19.1
ProcVersionSignature: Ubuntu 3.5.0-31.52-generic 3.5.7.11
Uname: Linux 3.5.0-31-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.6.1-0ubuntu10
Architecture: amd64
Date: Wed May 29 11:10:30 2013
EcryptfsInUse: Yes
InstallationDate: Installed on 2012-01-25 (489 days ago)
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111012)
MarkForUpload: True
SourcePackage: gnome-control-center
UpgradeStatus: Upgraded to quantal on 2013-05-10 (18 days ago)
usr_lib_gnome-control-center:
 activity-log-manager-control-center 0.9.4-0ubuntu4.2
 deja-dup 24.0-0ubuntu2
 gnome-control-center-signon 0.0.18-0ubuntu1
 indicator-datetime 12.10.2-0ubuntu3.1