Continuity mistake: Hugh Jackman puts a tan vest on twice in the scene when we first meet his wife.
Continuity mistake: When the hotel clerk show Angier Tesla's machine in its box, he has his hands behind his back, and then moves them in front of his body. Yet when the camera cuts to behind the clerk, his hands are still held behind him.
Answer: Angier always wants to take revenge on Borden as he is the reason behind the death of his wife. He knows that Borden is in the crowd the two times, first time, Olivia suggests Borden to watch the new "Transported Man" trick of Angier, where Borden finds out the trap door in the bottom of the machine, second time, Borden wants to know how Angier flies that distance with in seconds through the trap door. As expected by the Angier in the final play, Borden reaches the back stage where actual Angier is drowning (it is as always actual Angier drowns and the replica of Angier appears at some distance in every performance). So, as per the plan the replica hides to create an impression that Borden intentionally murders Angier. Note: the replica of Angier has the same ability and sense like actual Angier.
Rajesh v
It's never stated whether the "real" Angier drowns or takes the bow, but it's implied that it doesn't matter - as the clone is a perfect copy, they are both "Angier." Angier at one point says, referring to toll the trick has taken on him, that each time he did it, even he himself didn't know whether he would be the man in the box or the prestige. Similarly, when Angier asked Tesla which hat of all the duplicates was his, Tesla replied "They are all your hat."