Lightdm crashes on login

[Alvin]

After boot, I see a glimpse of a KDE bug report window. Then the screen goes blank.
Restarting lightdm results in either:
- the same (glimpse of bug, or blank)
- an actual greeter. It is possible to log in, but there's a message about kwin crashing to much.
Result: I can't start KDE.

ProblemType: Bug
DistroRelease: Ubuntu 13.10
Package: lightdm-kde-greeter 0.3.2.1-1ubuntu3
ProcVersionSignature: Ubuntu 3.11.0-14.21-generic 3.11.7
Uname: Linux 3.11.0-14-generic x86_64
ApportVersion: 2.12.5-0ubuntu2.1
Architecture: amd64
Date: Thu Dec 5 10:19:11 2013
InstallationDate: Installed on 2013-05-22 (197 days ago)
InstallationMedia: Kubuntu 13.04 "Raring Ringtail" - Release amd64 (20130424)
MarkForUpload: True
SourcePackage: lightdm-kde
UpgradeStatus: Upgraded to saucy on 2013-10-02 (63 days ago)