AI and revolts

rock

springs revolted (back ground) Rock Springs is garrisoned with my L-1 SP Rocket morale is at 25% and is surrounded by 6 provinces that I own morale is now 30-37% closes 2 friendly provinces current morale 50%56% Province revolts to my friend and its Morale goes up to 68% can someone tell me how this could happen he never owned the province or is this a bug