I think I'm able to reproduce more or less this same bug. For me, it occurs only when I use gnome-control-center to switch from VGA-off-and-LVDS-on directly to VGA-on-and-LVDS-off. If I start with both displays on, and disable LVDS, it works fine. If I use xrandr, it works fine. See bug #737891 (set as a dupe of this one now) for details.
For diagnosing, I used 'xrandr --verbose', which indicates some difference in how the crtcs are being mapped. I also enabled graphics debugging (sudo xdiagnose, first checkbox, apply, reboot), then collected dmesg before and after doing the switch, once with gnome-control-center, and once with xrandr. I will attach both of these files. (The logs fill with pipe A underrun messages which I believe to be irrelevant so have filtered those out for clarity.) ** Attachment added: "Broken case - using gnome-control-center" https://bugs.launchpad.net/ubuntu/+source/gnome-control-center/+bug/828623/+attachment/2467494/+files/dmesg.broke.clean.txt -- You received this bug notification because you are a member of Desktop Packages, which is subscribed to gnome-control-center in Ubuntu. https://bugs.launchpad.net/bugs/828623 Title: [Regression] gnome control centre does not allow you to disable the laptop screen while leaving an external DisplayPort connected screen working Status in GNOME Control Center: Unknown Status in “gnome-control-center” package in Ubuntu: Triaged Status in Fedora: Unknown Bug description: Lenovo T500 with displayport has a 1920x1200 monitor attached, I use the displayport in a similar way to a docking station in that I attach the monitor with a displayport to dvi cable, and then expect to be able to switch off the laptops internal display, only leaving the external monitor working. Screen detection works fine, mirrored screen works fine, but disabling the internal display and activating the external display just leads to the screen going black until the timeout has been reached, whereupon it reverts to its previous setting. This is a fully updated oneiric install ProblemType: Bug DistroRelease: Ubuntu 11.10 Package: gnome-control-center 1:3.1.4-0ubuntu5 ProcVersionSignature: Ubuntu 3.0.0-8.11-generic 3.0.1 Uname: Linux 3.0.0-8-generic x86_64 Architecture: amd64 Date: Thu Aug 18 10:35:59 2011 EcryptfsInUse: Yes InstallationMedia: Ubuntu 11.10 "Oneiric Ocelot" - Alpha amd64 (20110803.1) ProcEnviron: LANGUAGE=en_GB:en PATH=(custom, user) LANG=en_GB.UTF-8 SHELL=/bin/bash SourcePackage: gnome-control-center UpgradeStatus: No upgrade log present (probably fresh install) To manage notifications about this bug go to: https://bugs.launchpad.net/gnome-control-center/+bug/828623/+subscriptions -- Mailing list: https://launchpad.net/~desktop-packages Post to : desktop-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~desktop-packages More help : https://help.launchpad.net/ListHelp
