Shutdown during apt update with update manager results into fail of Xorg

[typo]

1. I clicked on the "update manager"
2. I saw some security updates of apt (bug #1013128)
3. I clicked on "install updates"
4. I clicked on "shutdown" some seconds later, but before the update was finished
5. I started the computer again
6. There was an unusable Xorg help assistent which did not recognize my keys. The window moved hackly from top to bottom or the other way around if I moved my mouse.
7. I killed Xorg using the text terminal and executed "startx"
8. I got a message: The session "ubuntu" was not able to load.
9. I excuted "sudo apt-get upgrade" to continue with the update. This worked smootly without any error message.
10. I tried to start X again, but it failed (message about that "ubuntu" session was not able to load)
11. I rebooted the machine
12. First LightDM appeared, I entered my password and then I used my GNOME Shell and Firefox to report a bug about what just happened.

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: update-manager 1:0.156.14.5
ProcVersionSignature: Ubuntu 3.2.0-25.40-generic 3.2.18
Uname: Linux 3.2.0-25-generic x86_64
NonfreeKernelModules: nvidia
ApportVersion: 2.0.1-0ubuntu8
Architecture: amd64
Date: Fri Jun 15 22:49:05 2012
EcryptfsInUse: Yes
GsettingsChanges:
 com.ubuntu.update-manager first-run false
 com.ubuntu.update-manager launch-time 1339792865
 com.ubuntu.update-manager show-versions true
 com.ubuntu.update-manager window-height 652
 com.ubuntu.update-manager window-width 872
InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Release amd64 (20111011)
PackageArchitecture: all
SourcePackage: update-manager
UpgradeStatus: Upgraded to precise on 2012-04-17 (59 days ago)