LightDM package fails to remove if lightdm user is in use

[Piotr Gajdowski]

After installing new updates op Ubuntu 12.04, lightdm stopped working properly, I can loggin but after that it only shows my wallpaper and my cursor. Sometimes I am unable to login.

I can however right click my desktop and go to settings etc, but the graphics are extremely laggy (for example moving a window).
But I can't see my desktop menu bar or anything else.

ProblemType: Package
DistroRelease: Ubuntu 12.10
Package: lightdm 1.4.0-0ubuntu2
ProcVersionSignature: Ubuntu 3.5.0-23.35-generic 3.5.7.2
Uname: Linux 3.5.0-23-generic x86_64
ApportVersion: 2.6.1-0ubuntu10
AptOrdering:
 ubuntu-desktop: Purge
 lightdm-remote-session-uccsconfigure: Purge
 lightdm-remote-session-freerdp: Purge
 lightdm: Purge
Architecture: amd64
Date: Tue Jan 29 22:29:00 2013
ErrorMessage: subprocess installed post-removal script returned error exit status 1
InstallationDate: Installed on 2013-01-16 (13 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release amd64 (20121017.5)
MarkForUpload: True
SourcePackage: lightdm
Title: package lightdm 1.4.0-0ubuntu2 failed to install/upgrade: subprocess installed post-removal script returned error exit status 1
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Robert Ancell (robert-ancell)]

From the terminal log:

Purging configuration files for lightdm ...
Removing user `lightdm' ...
Warning: group `lightdm' has no more members.
userdel: user lightdm is currently logged in
/usr/sbin/deluser: `/usr/sbin/userdel lightdm' returned error code 8. Exiting.
dpkg: error processing lightdm (--purge):
 subprocess installed post-removal script returned error exit status 1

Which indicates that LightDM was probably removed while it was running.

We should probably just warn if this occurs with the penalty that a lightdm user will be left on the system.