The Housemates make the show, the twists get in the way.

well its not meant to be the Bourne Identity now is it, its a bit of fun. Just enjoy it

If they really wanted the twist to work they would have prepared the 'Others' by telling them that they were to pretend to be new HM's while performing a secret task.

Instead they misled them (stir up the house and create paranoia) and then told them in the high stress of the crowd what they were supposed to do and that is pretend to be 'New Housemates' like you know nothing of what has been going on. -For that you would have needed a very good actor to pull it off. IMHO.

BB know the psychology so either they were badly advised or it is a foul up.
I think it is deliberate to get public reaction and interest.