Description of problem:
This is a bit of a weird issue.  I'm using an ATI video card with dual outputs.  Certain use patterns of gnome-display-properties cause things to break.

First, I can produce the desired results by following these steps:
1. run gnome-display-properties
2. uncheck "Mirror Screens"
3. move the blue screen icon to the right and click Apply.

By following those steps, I move the DVI-0 output to the right, producing a wide multihead desktop.

However, if I don't know that I'm supposed to do that (perhaps because the outputs aren't labelled in g-d-p) I might follow these steps instead:
1. run gnome-display-properties
2. uncheck "Mirror Screens"
3. move the blue screen icon to the left and click Apply.
   - this makes the DVI-0 output the "left" desktop area.  
   - DVI-0 is now represented by a green icon instead of its 
     original blue, which is odd.
   - I actually wanted the DVI-0 output to be the right area of the desktop.
     I figure out that the left desktop area is on the right physical monitor,
     so I want to move the left monitor icon to the right, in order that it
     will display the right desktop area.
4. move the green icon (DVI-0, displaying the left desktop area) to the right
   of the blue icon.
   - this makes the DVI-0 the "right" monitor.  It is represented by the 
     a blue icon again.
   - both physical displays are mirrored, with the contents that should be on
     the DVI-0 output

Version-Release number of selected component (if applicable):
control-center-2.24.0.1-7.fc10.x86_64
xorg-x11-drv-ati-6.9.0-25.fc10.x86_64
xorg-x11-server-Xorg-1.5.2-2.fc10.x86_64


How reproducible:
Always

Actual results:
The physical displays are mirrored, even though they're configured to be a wide multihead desktop.