When you press Shift+T instead of T, you are only sending messages to other players with the same (#%2) as yourself. So, if you're the server, team chat will communicate with players 3, 5, 7 and so on, regardless of their actual team. The original article explaining Team Chat can be found here.
As for the text disappearing bug... that happens if you're backspacing an old message, backspace past the first character, and then try to type a new message instead of just pressing Esc and T.