"The new ending has them getting back together in the end. It should really be called 'The Make Up,' " snickered the source.

"People want to see Jennifer happy after she was thrown over by Brad Pitt for Angelina Jolie," added another insider. "And with the original ending - well, it was just too much of the same."

A rep for Universal says: "Every film can benefit from a few extra days of shooting, and 'The Break Up' was able to return to Chicago for some quick additions that we believe will add to what we know is already an enormously satisfying movie."

While in Chicago, Aniston and Vaughn, according to witnesses, have also been house hunting and checking out luxury penthouse pads in the city Aniston seems to want to call home.