Possible incorrect assembly of the park brake mechanism. It is possible for the parking pawl to not engage and for the vehicle to roll down a slope when parked posing an increased risk of accident or injury.
What to do...
Contact your nearest Honda Motorcycle Dealer. Until you can have this problem rectified please use extra caution such as finding a flat area to park. If you must park on a slope, chock the wheels or try angling across a slope if it can be done safely so the vehicle is less likely to roll away.