I am not sure what caused this problem, as it was working nicely before... Yesterday I realized that one could not see the avatar selection widget anymore: I disabled/uninstalled AS, then reinstalled and regenerated all the avatars, but the problem was still there. So I started playing around with configuration: and found out that unchecking the "Enable unique avatars" flag would bring back the avatars. It looks like the system "believes" that there are no available avatars left, even if there are hundreds of those. What marks an avatar as "taken"?