A law has to be uniform. For instance, always, LBW has meant a decision of out given when the umpire deems the ball will hit the stumps.
However, when the referal is made, the uniformity of the law ends. If it clips, and the umpire had initially ruled it out, it remains out. However, if it clips, when the umpire had initially ruled not out, it remains not out. The decision made should be based on evidence and regardless of what the on field umpire had ruled earlier.
The current procedure isn't correct imo.