Migrating my standard "teaching room" build of Ubuntu (with the xubuntu package installed, so possibly I should describe it as Xubuntu) from 14.04 to 16.04. I've found several differences, including this one
The default desktop configuration file is no longer
/etc/xdg/xfce4/xfconf/xfce-perchannel-xml/xfce4-desktop.xml
but is instead
/etc/xdg/xdg-xubuntu/xfce4/xfconf/xfce-perchannel-xml/xfce4-desktop.xml
In order to provide every user with the same default desktop I copy in a version of the first file. Under 16.04 the user's background is the default XFCE wallpaper. So now I copy in the second file and everything is as it was.