Not willing to leave well enough alone, I made a slightly extended clip from that slip: I've slowed it down a bit, but you can see that first she loses the strap on her right shoulder, then her left shoulder then she really shakes her tits until she loses her top. I think she is most surprised by the fact then when she tries to force the straps up by lifting her arms, her top instead jams under her breasts. The whole sequence of losing her top and covering her breasts is bang bang bang. Just over a second really. They could of easily edited this whole sequence out. But they didn't. Another reason I think it isn't entirely an accidental slip. The movie says it was encoded 2006-08-19 and I see no reason to think it was very far off from when this was recorded.