There are inconsistencies within National Hockey League officiating, but the game moves so fast sometimes a review is required and the call is reversed. However, it's not very often a review of a major penalty is reviewed, than overturned.
Friday night during the Panther and Bruins Game 6 Florida's Carter Verhaeghe was originally assessed a major penalty due to what the referee believed was a hit to the head of Boston's Justin Brazeau. While the play looked close, the referee reviewed it and overturned the original call.