Unplugging a secondary monitor bypasses the lock screen

[Ryan Prichard]

I have a computer set up with two monitors (Acer and Hitachi).

If the screen is locked, I can unlock it in two steps:
1. Switch to VT7 (Ctrl-Alt-F7).
2. Reach behind the Hitachi monitor and pull out the DVI cable.

At this point, the session is unlocked -- I can see the left 2/3rds of the desktop, and the keyboard and mouse work. The right 1/3 is still black (perhaps covered by the lock screen?), and every few seconds the computer switches back to VT8. I can fix both problems with "killall light-locker".

Details:

The Acer is positioned to the right of the Hitachi. If I put it on the left instead, the bypass does not work.

Monitor models:
 - (primary) DVI-I-1: Acer P243W 24"
 - (secondary) DVI-I-2: Hitachi CML174SX 17"

Video card: EVGA 896-P3-1170-AR [GeForce GTX 275]
Video card driver: Nouveau
Motherboard: MSI P55-GD65

I have display compositing turned off (Window Manager Tweaks -> Enable display compositing), because when I had it turned on, the screen filled with garbage every few hours/days. Turning it off fixed that problem. I turned compositing back on to test this issue, and it still reproduced, but differently:
 - When I unlock the screen, the right 1/3 is still obscured as before, but,
 - The left 2/3 of the screen is also black, but my mouse cursor is visible in this region.
 - I can right-click and see a popup menu. I click "Open Terminal Here".
 - I can't see the terminal, but I can type "killall light-locker" to complete the unlock.

I wonder if there are similar bugs involving only a single monitor, or which involve attaching a new monitor.

ProblemType: Bug
DistroRelease: Ubuntu 14.04
Package: light-locker 1.4.0-0ubuntu1
ProcVersionSignature: Ubuntu 3.13.0-48.80-generic 3.13.11-ckt16
Uname: Linux 3.13.0-48-generic x86_64
ApportVersion: 2.14.1-0ubuntu3.8
Architecture: amd64
CurrentDesktop: XFCE
Date: Sun Apr 5 03:05:18 2015
InstallationDate: Installed on 2014-07-15 (263 days ago)
InstallationMedia: Xubuntu 14.04 LTS "Trusty Tahr" - Release amd64 (20140416.2)
SourcePackage: light-locker
UpgradeStatus: No upgrade log present (probably fresh install)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.

[Theo Linkspfeifer (lastonestanding)]

Sadly, there has not been any activity in this report. However, it is very likely that this security issue is fixed in newer Xubuntu releases.

Please let us know if this is the case.

[Launchpad Janitor (janitor)]

[Expired for light-locker (Ubuntu) because there has been no activity for 60 days.]