After a network disconnection the contact is still available.
1- Have 2 users connected A and B in different hosts. Users can see each other.
2- Cut internet connection for user A.
3- The user is still connected even after 16'
4- User B can send messages to user A
5- When user A comes back it does not receive any message.
More problem sources: http://www.igniterealtime.org/forum/thread.jspa?threadID=25082&tstart=0