I helped out for a few boards.

I have helped out for a board or two, the original player is now back but I cannot leave the Tourney - every time I go to the lobby, I find myself sitting down at a table in the Tourney
When the auto-movement is set, the server will move players until each player has finished all allocated boards in the tourney (at the right table and seat).
The only way to leave the Tourney before finishing all boards is to "Exit the Club", so the 'original' player can take his/her seat.