[Natty] X11 dead when exiting KDE if using KDM, but OK if using GDM

Hi,

On a Packard-Bell Easynote M1800 with as video:

01:00.0 VGA compatible controller: VIA Technologies, Inc. CN400/PM800/PM880/PN800/PN880 [S3 UniChrome Pro] (rev 02)

Noticed that, if using KDM, exiting KDE causes a "black screen" situation from which the only possible exit is by using the Evil Power Button.

If using GDM instead of KDM, no problemo, it rocks.

ProblemType: Bug
DistroRelease: Ubuntu 11.04
Package: kdm 4:4.6.2a-0ubuntu5.1
ProcVersionSignature: Ubuntu 2.6.38-10.46-generic 2.6.38.7
Uname: Linux 2.6.38-10-generic i686
Architecture: i386
Date: Fri Jul 22 16:09:10 2011
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Release i386 (20110427.1)
ProcEnviron:
 LANGUAGE=fr_FR:en
 LANG=fr_FR.UTF-8
 SHELL=/bin/bash
SourcePackage: kdebase-workspace
UpgradeStatus: No upgrade log present (probably fresh install)