Thanks for attaching the dmesg output with debugging turned on. Looking through it I do notice this bit which looks possibly complicit in this issue:
[ 515.630872] [drm:intel_prepare_page_flip], preparing flip with no unpin work? [ 515.683339] [drm:intel_wait_for_vblank], vblank wait timed out [ 515.683439] [drm:drm_crtc_helper_set_config], [ 515.683445] [drm:drm_crtc_helper_set_config], [CRTC:4] [NOFB] [ 515.683457] [drm:drm_crtc_helper_set_config], [CONNECTOR:5:LVDS-1] to [CRTC:3] [ 515.683463] [drm:drm_crtc_helper_set_config], crtc changed, full mode switch [ 515.683468] [drm:drm_crtc_helper_set_config], [CONNECTOR:11:VGA-1] to [NOCRTC] [ 515.692792] [drm:intel_crtc_cursor_set], [ 515.699776] [drm:i915_get_vblank_timestamp], crtc 1 is disabled [ 515.716486] [drm:i915_get_vblank_timestamp], crtc 1 is disabled [ 515.733167] [drm:i915_get_vblank_timestamp], crtc 1 is disabled ... Those crtc 1 disabled messages go on for almost 20 seconds, so I presume this sequence corresponds to when your screen was blanked. Looks like at that point the LVDS was mapped to crtc 3; perhaps X was expecting it on crtc 1 instead and started issuing the warnings when it didn't find it there. Would you be willing to do a quick check that this same behavior occurs in Ubuntu Precise? It should be sufficient to boot a Live USB session, configure the monitors, and see if it is working properly now. You can get the current Live USB desktop image at http://cdimage.ubuntu.com /daily-live/current/ and create a USB boot drive using usb-creator. ** Changed in: xorg-server (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Desktop Bugs, which is subscribed to gnome-control-center in Ubuntu. https://bugs.launchpad.net/bugs/840974 Title: configuration of external monitor on laptop does not work properly To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gnome-control-center/+bug/840974/+subscriptions -- desktop-bugs mailing list desktop-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/desktop-bugs