As I said, I think Hooper was delaying the penalty until the review was over and when he blew the whistle it was to reverse the decision but Vydra thought it was the penalty to be taken and so started his run-up.
Sean Dyche suggested the referee should hold the ball whilst the VAR review is ongoing. I suppose it could make it clearer although equally it would result in slight delays if he then got the all clear because they'd have to set up the set piece.