Arch Linux

Setup: a laptop with a LCD plugged in via VGA (the same happens with the HDMI output). It's an Intel Core i5 430M. It's a Nvidia Optimus (GeForce GT 335M) laptop, but the card being used is the Intel one. Nvidia is turned off, actually (happens when it's on, anyway).

Problem:

Having only one monitor active and switching completely to the other one. Example: Laptop screen on; change the settings so that the laptop screen is disabled and the external is activated. The screen becomes blank (but the mouse/pointer still appears). It happens both aways.

However, this works flawlessly in KDE 4.5. I assume they use some different independent method to deal with this. It doesn't work at least in Gnome and in Openbox, from what I can tell. It also works perfectly fine with the LTS kernel (2.6.32.20). It used to work fine with 2.6.34. I am not sure exactly when it did stop working, since I've been using KDE lately, but I believe it wasn't with the change to 2.6.35 (when was the switch exactly?). I think it was with either the 2.6.35.4 or .3. I don't recall exactly.

What works with kernel 2.6.35.4:
a) Having the two monitors active at the same time
a) Having the two monitors active at the same time and then deactivating one of them.
c) If, after reproducing the problem, I press ctrl+alt+fx and then press ctrl+alt+f7 back to X, the previously black screen is "recovered". It would be a workaround if the deactivated monitor didn't remain active with a tty (altough inoperable).

Steps to reproduce:

A)
i) Monitor A and B active.
ii) Deactivate Monitor B and keep Monitor A active (works).
iii) Deactivate Monitor A and activate Monitor B (blank screen except for mouse pointer).
iv) If you press ctrl+alt+f1 and then ctrl+alt+f7 the screen (Monitor B) is recovered.
v) Deactivate Monitor B and activate Monitor A (works). Some strange kind of memory from step i+ii?

B)
The same thing, just invert A and B in the step-sequence A), so that B is active and A is deactive in step ii.

I'm not that familiar with the inner works of KDE, but since it works with KDE under 2.6.35.4 and since it used to work fine in older kernels and still works fine with the lts kernel, could it be something else other than the kernel?

Additional info:

* package version(s)
kernel26 2.6.35.4-1
kernel26-lts 2.6.32.20-1
xorg-utils 7.6-3

* config and/or log files etc.

Attached is Xorg.0.log trimmed and divided by steps and the full Xorg.0.log
Also, the /etc/X11/xorg.conf.d/10-monitor.conf that is currently being used, that still works under kernel26-lts and used to work ond previous kernel26.
Nothing at all turns up in /var/log/messages when those steps are reproduced.