Perhaps they did. Her statement today fits right in with his use of the phrase 'wardrobe malfunction'.
Here's my take on the whole thing. And I only suspected this until Jackson issued her statement today...now I'm sure of it.
It was to be just as Janet says it was. They planned something of a costume reveal for the end of her segment. The problem is, the costume designer who was in on the secret either screwed up or has pulled of a huge on both of them. It may be that the portion of her costume that was to pull away when Justin applied the proper pulling action was the midriff section, leaving her breasts covered...or perhaps only the black leather top layer was to come off leaving the red lacey portion in place.
I believe that unknown to them, the "seamstress" who built the thing decided to have some fun and work it so that the right cup was the only thing to pull away. It is also possible that the thing didn't work as designed and JJ wound up exposed.
I have seen the video many times and the look on her face tells me that she was mortified and thunderstruck. She had been 'had'.
We shall see what comes out later on but there is much more to this story than anyone knows or is talking about right now. Just my humble opinion.