Comment 8 for bug 116107

Both Tom's and Sherradb's solutions worked for me, I'm very happy :)

Just one remark about Sherradb's one: don't forget
sudo chmod a+x /etc/erwise acpi/asus-display-switch.sh
otherwise it won't work.
Also, after he first cycle the behaviour becomes more irregular, but not at a problematic extent: it sometimes displays both when it should display only one