after switch to kdm, lightdm starts and stops at boot

[pp]

lightdm was installed on my system, after it came with kubunut release upgrade.
I set kdm as standart display manager again, by dpkg-reconfigure kdm.

all went fine, and kdm works properly.
recently i noticed that lightdm is started at boot, just to become stopped right after that. i searched for, but did not find any sense for this behavior.

boot.log:
 * Starting LightDM Display Manager^[[174G[ OK ]
 * Stopping LightDM Display Manager^[[174G[ OK ]

i think lightdm sould not even be started, after i set an other default display manager.

ProblemType: Bug
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 i686
ApportVersion: 2.6.1-0ubuntu10
Architecture: i386
Date: Mon Feb 4 12:45:42 2013
InstallationDate: Installed on 2011-11-11 (450 days ago)
InstallationMedia: Kubuntu 11.10 "Oneiric Ocelot" - Release i386 (20111011)
MarkForUpload: True
ProcEnviron:
 LANGUAGE=de_DE
 TERM=xterm
 PATH=(custom, no user)
 LANG=de_DE.UTF-8
 SHELL=/bin/bash
SourcePackage: lightdm
UpgradeStatus: Upgraded to quantal on 2012-11-13 (83 days ago)

[Launchpad Janitor (janitor)]

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

[Ivo Roghair (ivo-82)]

Also the case for a fresh 12.10 installation with gnome-shell and gdm as default.

/var/log/boot.log shows
 * Starting LightDM Display ManagerESC[74G[ OK ]
 * Stopping LightDM Display ManagerESC[74G[ OK ]

At the time that happens, gdm has already been started.