I 've been looking at this problem and the results so far are:
- IE6/win is removed normally after 2 * chat_old_ping seconds.
- Firefox1.0/win is usually removed after the same period. I say "usually" because I 'm getting some strange behavior (When I click the link, two popups open. If I close both, one of them is removed always but the second isn't always detected when it disconnects...)