The only thing that comes to mind is that perhaps that happens because the person on his list has put him on "appear permanently offline" and it has been known in Yahoo Messenger to show you at first when you log on or off. For example there are times I am on invisible and if I log off people see my name log off and hear the door sound even though I am invisible. The strange thing with his situation is that (and if I undestand correctly) he doesn't see anything come up on his yahoo like a little box with a name?