After removing second display: Single display setup not remembered

Question

I recently removed one display from a dual head display setup.

Everything works fine, but after I wake up from standby the picture seems to be shifted to the left (were my second display was) about the width of the removed display. The corresponding right area of the display is then unused (black).

This does only happen after leaving standby.

After login, I blindly change the display settings to another resolution and then back to the previous value. That makes the picture shift back into the right position. But this setting is not remembered!

How can I get it to remember that the second display was removed?

EDIT: The content of my xorg.conf:

Section "ServerLayout"  
    Identifier     "aticonfig Layout"  
    Screen      0  "aticonfig-Screen[0]-0" 0 0  
EndSection 

Section "Module"
EndSection

Section "Monitor"
    Identifier   "aticonfig-Monitor[0]-0"
    Option      "VendorName" "ATI Proprietary Driver"
    Option      "ModelName" "Generic Autodetecting Monitor"
    Option      "DPMS" "true"
EndSection

Section "Device"
    Identifier  "aticonfig-Device[0]-0"
    Driver      "fglrx"
    BusID       "PCI:1:0:0"
EndSection

Section "Screen"
    Identifier "aticonfig-Screen[0]-0"
    Device     "aticonfig-Device[0]-0"
    Monitor    "aticonfig-Monitor[0]-0"
    DefaultDepth     24
    SubSection "Display"
        Viewport   0 0
        Depth     24
    EndSubSection
EndSection