Can't unlock session when external monitor disconnected

[Martin Magnusson]

Sometimes I have the problem that I can't unlock my session (for example, after resuming from suspend). The problem seems to be related to my dual head setup. I have a laptop (the primary monitor) and an external VGA monitor.

When I got this problem yesterday, at home, I couldn't log in to my session. I typed my password in the box, black dots showed up, but when I hit "enter" or "unlock", nothing happened. I could, however, log in to a terminal (alt-F5 for example). I couldn't find any output relating to login in auth.log or syslog.

When I suspended the computer, the external monitor was plugged in. When I resumed at home, it was disconnected.

Today, connecting the external monitor at work, and resuming again, I noticed that the login box on the laptop display had the black dots in it from yesterday, but there was another login box at the VGA monitor which was empty. I typed in my password on the external monitor instead, and then I could log in.

I'm running Kubuntu 13.04, with lightdm 1.6.0-0ubuntu3.

ProblemType: Bug
DistroRelease: Ubuntu 13.04
Package: lightdm 1.6.0-0ubuntu3
ProcVersionSignature: Ubuntu 3.8.0-29.42-generic 3.8.13.5
Uname: Linux 3.8.0-29-generic i686
ApportVersion: 2.9.2-0ubuntu8.3
Architecture: i386
Date: Wed Aug 21 09:13:56 2013
InstallationDate: Installed on 2013-04-29 (113 days ago)
InstallationMedia: Kubuntu 13.04 "Raring Ringtail" - Release i386 (20130424)
LightdmConfig:
 [SeatDefaults]
 user-session=kde-plasma
 greeter-session=lightdm-kde-greeter
MarkForUpload: True
SourcePackage: lightdm
UpgradeStatus: No upgrade log present (probably fresh install)