Why are my display settings not persistent?

So this is probably more technical than a good solution would be, but if all else fails you can execute this code in a terminal (with your external monitor plugged in):

if [ "$(xrandr|grep -c 'connected')" > 2 ]; then xrandr --output LVDS1 --mode 1920x1080 --right-of VGA1; xrandr --output VGA1 --mode 1920x1200; fi

This will use xrandr to readjust your monitor settings.

You could also look into getting this to run automatically when you log in.

I would wait a little bit to see if someone comes up with a better solution.

p.s. you can replace --right-of in the command with --left-of depending on which side you have your laptop on.