I've been walking through Semos many times today without any problem. Then I stayed inside the bank for a while and when I came out, I saw the missing gfx. (See screenshot: http://imagebin.org/186979\)
After renaming the cache folder (Semos city files attached to the artifact), the problem was gone.
Annotation: I've had no connections to other servers at the same time (but yesterday), but I've had multiple clients online on the main server.