I tried uploading a very small avatar again (9.63kB) and the same thing happened again: the system acknowledges that the profile has been updated, but the avatar is actually nowhere to be found.
I can certainly live with it myself for the time being (and it must be awkward for you looking after things without all the permissions), but thought it might be useful in diagnosing the problem if I just described what happened.
Another problem I am not sure who to contact about is that
the Sierra Forums gateway seems to have been down for a couple of days now.