Although there's a message about this automatically shown when you first log into the game, I figured some people may have missed it or not understood it. There's a bug in the latest patch that causes people who log off or are disconencted durring TFs, SFs, and trials to be booted from the team they're on. You can read about it here (http://www.cityofheroes.com/news/known_issues.html).
I'm cross-posting this in the CoH/CoV General Discussion, Open Events, and Callboard forums, as it seems to relate equally to all of these.
Today's patch is supposed to have fixed this problem.