The 'spacefun-wallpaper.svg' was the only background
available, ,and then only because it is default. Every other
background that is in the list resides in
'/usr/share/backgrounds/gnome'.
When I tried to add any of the .svg backgrounds
(i.e. 'moreblue-orbit-wallpaper.svg') the file chooser showed a '?'
symbol,
whereas selecting one of the .png files gives a thumbnail view of the
background. After selecting an .svg file to add, the resulting choice
showed a solid green background in the list of choices (no background).
I realize this is a probably a corner case, after all the other
machine
I administer is able to display the background just fine. After
upgrading
this system to the same level as the working one I expected this to be
fixed
(the upgrade included some gnome dependencies and inkscape), so
I guess I'll keep drilling and GDM, s and ltracing. Also I'll
reinstall
'gnome-control-center' and have a look at the
'gnome-appearance-properties'
source.