Some Users are shown as "offline"

hi,

have a strange problem. have setup ejabberd ejabberd-1.0.0 on a suse linux 9.3 server. some clients are psi (under windows) and some are kopete (under linux). when the users go on and connect to the ejabberd server, they don't see all users which are online. some are shown as offline and some are shown as online.

on the webinterface i see that all of the current online users are shown. but not on the clients.

is that a global problem of ejabberd or a configuration problem?

greetings

lin