Well maybe vbulletin cache's the query and makes the change later but displays the new one right now.
We query the vbulletin tables when someone views the photo and grab the avatar and display it based on whats retrieved from the vb
Now of course a computer cache's can cause a difference between users as well. We use no-cache headers though
Content visible to verified customers only.
So there should be no caching being done on our end but there are never absolutes.