From: Chris Jones <cjns1989@gmail.com>
I ran the above test and after grepping out the /sys & /proc's, I came up with just one file... Xorg.0.log..! So it looks like this setting is remembered somewhere outside the file system.
At least in my experience, xrandr modes are *not* remembered. I have to rerun it everytime X is started or configure Xorg.conf. Curious that in your system the settings persist.