I selected a theme, then went one changing one sound that belongs to it. The
sounds was from /usr/share/sounds. But g-s-p createed symlink pointing to the
filename without the /usr/share/sounds prefix, which of course doesn't work.
$ ll ~/.local/share/sounds/__custom/desktop-login.ogg
4.1k lrwxrwxrwx 1 hadess hadess 27 2008-07-28 17:53
Works fine here. Please test either upstream, or use "G_DEBUG=debug
gnome-sound-properties" to get a full debug.
Seems to work correctly with control-center 2.23.6