Dell 2405FPW not automatically configured, ugly display

xserver-xorg autoconfigures my new LCD screen at 1680x1680, which is not the
preferred or maximum resolution for the screen:

$ sudo xresprobe nv
Password:
id: DELL 2405FPW
res: 1680x1680 1600x1200 1280x1024 1152x864 1024x768 800x600 720x400 640x480
freq: 30-81 56-76
disptype: crt

I get the same output with the nvidia driver. However:

$ sudo ddcprobe
vbe: VESA 3.0 detected.
oem: NVIDIA
vendor: NVIDIA Corporation
product: NV36 Board - p222-2n Chip Rev
memory: 262144kb
mode: 640x400x256
mode: 640x480x256
mode: 800x600x16
mode: 800x600x256
mode: 1024x768x16
mode: 1024x768x256
mode: 1280x1024x16
mode: 1280x1024x256
mode: 320x200x64k
mode: 320x200x16m
mode: 640x480x64k
mode: 640x480x16m
mode: 800x600x64k
mode: 800x600x16m
mode: 1024x768x64k
mode: 1024x768x16m
mode: 1280x1024x64k
mode: 1280x1024x16m
edid: 1 3
id: a00f
eisa: DELa00f
serial: 32324a53
manufacture: 34 2005
input: separate sync, composite sync, sync on green, analog signal.
screensize: 52 33
gamma: 2.200000
dpms: RGB, active off, suspend, standby
timing: 720x400@70 Hz (VGA 640x400, IBM)
timing: 640x480@60 Hz (VGA)
timing: 640x480@75 Hz (VESA)
timing: 800x600@60 Hz (VESA)
timing: 800x600@72 Hz (VESA)
timing: 800x600@75 Hz (VESA)
timing: 1024x768@87 Hz Interlaced (8514A)
timing: 1024x768@75 Hz (VESA)
ctiming: 1280x1024@60
ctiming: 1600x1200@60
ctiming: 1152x864@75
ctiming: 1680x1680@60
dtiming: 1920x1200@59
monitorserial: P654058G22JS
monitorname: DELL 2405FPW
monitorrange: 30-81, 56-76

That shows the maximum resolution of 1920x1200 correctly.

Additionally, even after doing a thorough display calibration (with the nvidia
test image I showed you last week), the display is shadowed, like a badly tuned
TV. It's not unusable, but subtly ugly, and text is much harder to read. This
might be a separate bug. :-)