I left the client application running for a while, say 20 minutes, and it always gave name=0, width = 0, height = 0. However, it knows that there is a server sending out frames, because the hasNewFrame method returns true (I tried the client without any syphon server running, and never got any new frame notification, meaning that at least the notifications are not bogus).
Will look at the SyphonImage issues later.