my wallpaper seems different on login

I have a centered wallpaper, which is originally bigger than the screen resolution of a netbook. So I have changed the mod of showing up the wallpaper by gnome wallpaper settings.

There is a new feature in Ubuntu 12.04 that shows the wallpaper image on login. So when I welcomed, I realized that login does not show my wallpaper like on my desktop. I think there is a miscorolation between gnome wallpaper tool and login screen.

Thanks.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: ubuntu-desktop (not installed)
ProcVersionSignature: Ubuntu 3.2.0-10.18-generic-pae 3.2.1
Uname: Linux 3.2.0-10-generic-pae i686
NonfreeKernelModules: wl
ApportVersion: 1.91-0ubuntu1
Architecture: i386
Date: Fri Jan 27 08:37:25 2012
InstallationMedia: Ubuntu 12.04 LTS "Precise Pangolin" - Alpha i386 (20120104)
SourcePackage: ubuntu-meta
UpgradeStatus: No upgrade log present (probably fresh install)