You can try to edit /usr/share/xubuntu/session.sh, and add at the beginning (before the XDG_DATA_DIRS change):
if [ -z "$XDG_CONFIG_DIRS" ]; then XDG_CONFIG_DIRS="/etc/xdg/xdg-xubuntu" export XDG_CONFIG_DIRS fi
Xfce should then use the xubuntu settings in the xubuntu session.
You can try to edit /usr/share/ xubuntu/ session. sh, and add at the beginning (before the XDG_DATA_DIRS change):
if [ -z "$XDG_CONFIG_DIRS" ]; then DIRS="/ etc/xdg/ xdg-xubuntu"
XDG_CONFIG_
export XDG_CONFIG_DIRS
fi
Xfce should then use the xubuntu settings in the xubuntu session.