... yeah, some are worse than others from my memory. Even my Rebels or my son's Vegas did it in super light conditions, but usually only on the beach if memory serves me correct. I used to ride the Core XR17m and it flapped a bit, but again usually only in very under powered condtions.
Actually thinking about it now, I seem to remember all though they did flap on the beach in f all winds, it didn't really flap much once on the board. I'd say combined with the fact that the Vantage is a big kite, with 3 struts in light winds and on the beach, this will contribute to the extra flapping.
Of course I am only guessing here by the way, it migh do it all the time for all I know.
Cheers,
Robbie