You have it backwards. Patrolling (including Move & Patrolling) leaders do defend the province, all other leaders hide inside the castle. It does really work that way so whatever you are seeing, it probably isn't really there. :-)
"The difference between 'Patrol' and 'Defend' in a province with a fortress is that patrollers will engage in combat outside the fortress, while defenders will concede the province and become besieged."