sudo adduser foo --uid 998 crashes xorg

I can provoke the bug by running the following command in the gnome-termnial:
sudo adduser foo --uid 998
Sends me to the gdm.
Sounds pretty crazy to me, but I tried it several times always with the same results

I noticed the same behaviour when deleting a user with:
"sudo userdel foo"

ProblemType: Bug
DistroRelease: Ubuntu 12.04
Package: xorg 1:7.6+12ubuntu1
ProcVersionSignature: Ubuntu 3.2.0-31.50-generic 3.2.28
Uname: Linux 3.2.0-31-generic x86_64
NonfreeKernelModules: nvidia
.proc.driver.nvidia.version:
 NVRM version: NVIDIA UNIX x86_64 Kernel Module 173.14.35 Fri Jun 8 00:07:59 PDT 2012
 GCC version: gcc-Version 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
.tmp.unity.support.test.0:

ApportVersion: 2.0.1-0ubuntu13
Architecture: amd64
CompizPlugins: [core,composite,opengl,compiztoolbox,decor,vpswitch,snap,mousepoll,resize,place,move,wall,grid,regex,imgpng,session,gnomecompat,animation,fade,workarounds,scale,expo,ezoom]
CompositorRunning: compiz
Date: Fri Sep 28 15:23:28 2012
DistUpgraded: Fresh install
DistroCodename: precise
DistroVariant: ubuntu
ExtraDebuggingInterest: Yes,
GraphicsCard:
 NVIDIA Corporation C51 [GeForce 6150 LE] [10de:0241] (rev a2) (prog-if 00 [VGA controller])
   Subsystem: Dell Device [1028:01ec]
InstallationMedia: Ubuntu 12.04.1 LTS "Precise Pangolin" - Release amd64 (20120823.1)
JockeyStatus:
 xorg:nvidia_173 - Beschleunigter Grafiktreiber von NVIDIA (Proprietär, Aktiviert, In Benutzung)
 xorg:nvidia_173_updates - NVIDIAs beschleunigte Grafiktreiber (Nachträgliche Aktualisierungen) (Proprietär, Deaktiviert, Nicht benutzt)
 xorg:nvidia_current - Beschleunigter Grafiktreiber von NVIDIA (Proprietär, Deaktiviert, Nicht benutzt)
 xorg:nvidia_current_updates - NVIDIAs beschleunigte Grafiktreiber (Nachträgliche Aktualisierungen) (Proprietär, Deaktiviert, Nicht benutzt)
Lsusb:
 Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
 Bus 002 Device 001: ID 1d6b:0001 Linux Foundation 1.1 root hub
 Bus 002 Device 002: ID 045e:0752 Microsoft Corp.
 Bus 002 Device 003: ID 045e:00cb Microsoft Corp. Basic Optical Mouse v2.0
MachineType: Dell Inc. OptiPlex 740 Enhanced
ProcEnviron:
 LANGUAGE=de_AT:de
 TERM=xterm
 PATH=(custom, no user)
 LANG=de_AT.UTF-8
 SHELL=/usr/bin/zsh
ProcKernelCmdLine: BOOT_IMAGE=/boot/vmlinuz-3.2.0-31-generic root=UUID=9b3bcf9b-51c9-4816-8ec8-467d0f429913 ro quiet splash vt.handoff=7
SourcePackage: xorg
UdevDb: Error: [Errno 2] Datei oder Verzeichnis nicht gefunden
UpgradeStatus: No upgrade log present (probably fresh install)
XorgConf:
 Section "Device"
  Identifier "Default Device"
  Option "NoLogo" "True"
 EndSection
dmi.bios.date: 07/03/2008
dmi.bios.vendor: Dell Inc.
dmi.bios.version: 2.1.8
dmi.board.name: 0YP806
dmi.board.vendor: Dell Inc.
dmi.board.version: A00
dmi.chassis.type: 3
dmi.chassis.vendor: Dell Inc.
dmi.modalias: dmi:bvnDellInc.:bvr2.1.8:bd07/03/2008:svnDellInc.:pnOptiPlex740Enhanced:pvr:rvnDellInc.:rn0YP806:rvrA00:cvnDellInc.:ct3:cvr:
dmi.product.name: OptiPlex 740 Enhanced
dmi.sys.vendor: Dell Inc.
version.compiz: compiz 1:0.9.7.8-0ubuntu1.4
version.ia32-libs: ia32-libs 20090808ubuntu36
version.libdrm2: libdrm2 2.4.32-1ubuntu1
version.libgl1-mesa-dri: libgl1-mesa-dri 8.0.3+8.0.2-0ubuntu3.2
version.libgl1-mesa-dri-experimental: libgl1-mesa-dri-experimental N/A
version.libgl1-mesa-glx: libgl1-mesa-glx 8.0.3+8.0.2-0ubuntu3.2
version.nvidia-graphics-drivers: nvidia-graphics-drivers N/A
version.xserver-xorg-core: xserver-xorg-core 2:1.11.4-0ubuntu10.8
version.xserver-xorg-input-evdev: xserver-xorg-input-evdev 1:2.7.0-0ubuntu1.2
version.xserver-xorg-video-ati: xserver-xorg-video-ati 1:6.14.99~git20111219.aacbd629-0ubuntu2
version.xserver-xorg-video-intel: xserver-xorg-video-intel 2:2.17.0-1ubuntu4.1
version.xserver-xorg-video-nouveau: xserver-xorg-video-nouveau 1:0.0.16+git20111201+b5534a1-1build2