canberra-gtk-play refers to 'desktop-login' and 'desktop-logout' for the login and logout sounds.
gnome-audio is linking /usr/share/sounds/startup3.wav to /usr/share/sounds/login.wav instead of /usr/share/sounds/desktop-login.wav
(as referenced by /usr/share/gnome/autostart/libcanberra-login-sound.desktop)
and /usr/share/sounds/shutdown1.wav to /usr/share/sounds/logout.wav instead of /usr/share/sounds/desktop-logout.wav
(as referenced by /usr/share/gnome/shutdown/libcanberra-logout-sound.sh).

Note that even correcting the link to the shutdown sound won't make it work
but that isn't a bug of gnome-audio.

As an observation, I noticed that the upstream gnome-sound-theme ( http://git.gnome.org/browse/gnome-sound-theme/ )
use desktop-login and desktop-logout properly (but then its structure is quite different from the one from the gnome-audio package).