My laptop screen has a 1024x768 resolution, and attached to it is a 23" monitor set to a resolution of 1920x1080. Works beautifully; I can drag and drop anything between the two (in other words, I do NOT have the "same image in all monitors" option checked in Monitor Preferences).

The problem comes when turning the machine on: it can never figure out what the big monitor is (though it usually displays everything right for a few seconds), so it re-sets them both to the lower resolution and puts a checkmark in the "Same image in all monitors" preferences box.

There's obviously a setting that's screwed up here. Does anyone out there know what it might be?

kentfx

resolutions can be manualy set with xrandr on startup

example:
xrandr --output VGA1 --auto
xrandr --output LVDS1 --off --output VGA1 --mode 1152x864
xrandr --output LVDS1--off --output VGA1 --mode 1280x1024

your problem is probably occuring because in dual monitor setup, usually two same size monitors are used.