Problems with Xorg i810 driver, laptop and external monitor, and MergedFB

Hi,

I have a Dell XPs M1210 laptop with an intel video card. This works
fine with the laptop's flat panel display (1280x800) using the i810
driver once I've done a tweak with 915resolution.

However, I'd also like to get it working properly with an external LCD
display I have, and also with data projectors when I travel.

So, I investigated the MergedFB extension. This seems to succesfuly
send signals too the external monitor and the laptop display. However,
the external display (1280x1024) display is set at a too low
resolution, and the laptop display is just a mass of colours and
unreadable.

My xorg.conf is:
Section "InputDevice"
       Identifier  "Keyboard0"
       Driver      "kbd"
       Option      "XkbModel" "pc105"
       Option      "XkbLayout" "gb"
EndSection

Section "InputDevice"
       Identifier  "Synaptics"
       Driver      "synaptics"
       Option      "Device" "/dev/input/mice"
       Option      "Protocol" "auto-dev"
       Option      "Emulate3Buttons" "yes"
EndSection

Section "Device"
       Identifier  "Videocard0"
       Driver      "i810"
#       Option      "MergedFB" "true"
#       Option      "Clone" "true"
#       Option      "MonitorLayout" "LFP,CRT"
#       Option      "MetaModes" "1280x800-1280x1024 1280x1024-1280x1024"
EndSection

Section "Screen"
       Identifier "Screen0"
       Device     "Videocard0"
       DefaultDepth     24
       SubSection "Display"
               Viewport   0 0
               Depth     24
               Modes   "1280x1024" "1280x800"
       EndSubSection
EndSection

Section "ServerLayout"
       Identifier     "Default Layout"
       Screen      0  "Screen0" 0 0
       InputDevice    "Keyboard0" "CoreKeyboard"
       InputDevice    "Synaptics" "CorePointer"
EndSection

With the lines relevant to MergedFB commented out, I can successfully
fire up an X display on either the laptop of the external monitor by
switching to console mode and pressing Function-F8 (the CRT/LCD key on
this laptop). Pressing Function-F8 while looking at the Xsession
doesn't change the display, oddly.

Anyway, if I uncomment the MergedFB lines, the symtoms described above
are seen, and in the Xorg.o.log I see:

(II) I810(0): <default monitor>: Using default hsync range of 31.50-37.90 kHz
(II) I810(0): <default monitor>: Using default vrefresh range of 50.00-70.00 Hz
(II) I810(0): Not using mode "1280x1024" (no mode of this name)
(II) I810(0): Not using mode "1280x800" (no mode of this name)
(II) I810(0): MergedFBMonitor: Using default hsync range of 31.50-37.90 kHz
(II) I810(0): MergedFBMonitor: Using default vrefresh range of 50.00-70.00 Hz
(II) I810(0): Not using mode "1280x1024" (no mode of this name)
(II) I810(0): MergedFB: Generating mode list
(WW) I810(0): Mode "1280x800" is not a supported mode for First
(WW) I810(0):   (Skipping metamode "1280x800-1280x1024")
(WW) I810(0): Mode "1280x1024" is not a supported mode for First
(WW) I810(0):   (Skipping metamode "1280x1024-1280x1024")
(EE) I810(0): No modes. Disabling MergedFB.
(II) I810(0): Increasing the scanline pitch to allow tiling mode (800 -> 1024).
(--) I810(0): Virtual size is 800x600 (pitch 1024)
(**) I810(0):  Built-in mode "800x600"
(**) I810(0):  Built-in mode "640x480"
(II) I810(0): Attempting to use 60.32Hz refresh for mode "800x600" (852)
(II) I810(0): Attempting to use 60.00Hz refresh for mode "640x480" (850)
(==) I810(0): DPI set to (75, 75)

Any ideas as to why X is not finding the correct modes? X is bizarrely
refusing to use either 1280x800 or 1280x1024 mode.

Is MergedFB actually meant to work with i810?

Thanks,
Jonathan