Where does it say that players can only win on their turn (i.e. not during the Special Building Phase?) The Mayfair edition I've got doesn't have that rule.
In the Mayfair rules for the basic game (last copyright dated 2003), on page 8, under Winning the Game (End of Game): The first player to accumulate ten or more victory points during his turn immediately wins the game. (emphasis by me)
The key phrase is during his turn. This was not modified by the expansion game rules for the 5/6 player expansion. Also, the 5/6 player rules point out that the special building phase at the end of each player's turn does not constitute another player's turn.
If the rule was changed later, I am not aware of it, but it might be true. Anyway, this is the way we interpret the rule and play the game.
