This is from Yahoo news about that incident:
• I have never, ever heard as big a gasp in the press room as when the TV telecast cut to a reaction shot of Angelina Jolie and Brad Pitt during Jennifer Aniston's presenting gig. At first, I thought Aniston fell out of her dress. Or Jack Black fell into it.
It was just that the cameramen made a goal to get those two's reactions when JA was onstage...There was this whole controversy with that too, like, why she had to be there to present an award when she wasn't even nominated...people thought she would make herself look bad because Brangelina were both nominated...But some say that she's there to show that she's moved on and doesn't care about all that junk...