lightdm screen disappears and reappears in multi-monitor setup with different resolutions

[Rocko]

My laptop monitor is 1920x1080 and the external screen is 1680x1050, both driven through an intel chip (configured via xrandr in X sessions).

When lightdm's login greeter first appears, it displays in a 1680x1050 *centered* window. But a second or two afterwards, the screen disappears for half a second to a second and reappears as a left-aligned 1680x1050 window.

Everything still works, ie I can log in fine and no characters are lost from the password being entered, but it's a bit disconcerting because it initially looks like the login screen has crashed.

ProblemType: Bug
DistroRelease: Ubuntu 11.10
Package: lightdm 0.9.3-0ubuntu8
Uname: Linux 3.1.0-rc5-git-20110905.0929 x86_64
Architecture: amd64
Date: Mon Sep 5 21:51:38 2011
InstallationMedia: Ubuntu 11.04 "Natty Narwhal" - Beta amd64 (20110330)
SourcePackage: lightdm
UpgradeStatus: Upgraded to oneiric on 2011-09-02 (3 days ago)