It seems to me that this is Psi issue, not Tigase. When you have a contact in Psi and the contact is connected multiple times then once one of the connection goes offline, Psi displays the contact as offline, regardless other user's connections.

You can verify this by opening an XML console in Psi and watch incoming presence packets. If the buddy has many resources and only one unavailable presence for this user arrives, the buddy status is shown as offline in Psi, and on the XML console only one presence unavailable was received.

If I am wrong about the Psi client use case, please reopen the ticket.