Binary package hint: gnome-control-center
I have observed the problem when using my laptop (Compaq NC6220) with an external monitor or projector. It can be reproduced as follows:
1. Start with both screens in mirrored (clone) mode, and with no virtual resolution line in xorg.conf.
2. Open the screen resolution capplet.
3. Uncheck the "mirror screens" box. The screens are still displayed as a single one, that is, you still see only one of them even if they aren't in mirror mode anymore. This is confusing.
4. Click on the visible screen. This will move it under the other one, which should have happened in step 3, anyway.
5. Check the "mirror screens" box again. The screens come together again. Notice that this state should be exactly equivalent to the initial state, before opening the box.
6. Press the apply button. A message box appears stating that the virtual resolution must be changed, which is obviously not true since we didn't change anything. Accepting the dialog actually inserts some bogus "Virtual" line in xorg.conf.
This happened when using the capplet under intrepid beta (gnome-control-center 2.24.0.1).
[TEST CASE]
1. Start with both screens in mirrored (clone) mode, and with no virtual resolution line in xorg.conf.
2. Open the screen resolution capplet.
3. Uncheck the "mirror screens" box.
4. Click on the visible screen. This will move it under the other one.
5. Check the "mirror screens" box again. The screens come together again.
6. Press the apply button.
+ Expected behavior: Nothing. The "new" configuration is unchanged from the old one; there are no changes to apply. No dialogs should be displayed. The xorg.conf should be identical to before the test.
+ Actual behavior: A message box appears stating that the virtual resolution must be changed. After accepting this, the xorg.conf is modified with a bogus 'Virtual' setting.
To verify the fix, ensure that the Expected behavior described above is seen.
tseliot, could you take a look at this?