Comment 9 for bug 820327

It would also be useful to capture the X calls that gnome-settings-daemon makes. You should be able to do this by installing the ‘xtrace’ package, and running
"""
killall gnome-settings-daemon && xtrace -o ~/gnome-settings-daemon.xtrace /usr/lib/gnome-settings-daemon/gnome-settings-daemon
"""
at a terminal. This should kill the existing daemon and then start a new one, capturing all the X calls it makes to ~/gnome-settings-daemon.xtrace.

Then, cycle through the fn-f7 options again - both with the displays panel open, and without, so we get an example of both working and broken behaviour - and attach the ~/gnome-settings-daemon.xtrace file here.

If this is too complicated, the gsd-debug-randr.log file Sebastian was asking for above might contain enough information to debug this problem, so don't worry if it's too much effort.