Unable to change session/desktop environment if installed too many of those.

[Ｖ字龍(Vdragon)]

The new session selection UI of LightDM requires user to select their desired session -> click OK(?) to make effect, however if a user installs to many session/desktop environment, the list will become too long and it extends to outside of the screen
In this case there is no way choosing another session by mouse or keyboard.

ProblemType: Bug
DistroRelease: Ubuntu 12.10
Package: lightdm 1.4.0-0ubuntu2
ProcVersionSignature: Ubuntu 3.5.0-25.25-lowlatency 3.5.7.4
Uname: Linux 3.5.0-25-lowlatency i686
NonfreeKernelModules: nvidia
ApportVersion: 2.6.1-0ubuntu10
Architecture: i386
Date: Mon Mar 18 05:09:45 2013
InstallationDate: Installed on 2013-03-08 (8 days ago)
InstallationMedia: Ubuntu 12.10 "Quantal Quetzal" - Release i386 (20121017.2)
MarkForUpload: True
ProcEnviron:
 LANGUAGE=zh_TW:en
 PATH=(custom, no user)
 XDG_RUNTIME_DIR=<set>
 LANG=zh_TW.UTF-8
 SHELL=/bin/bash
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)

[Ｖ字龍(Vdragon) (vdragon)]

Here is a screenshot of what happens:(
I'm forced to switch to GDM now.