Commercial Pilot reported a parking brake malfunction while arriving at a ramp position after shutting down engines and attempting to set the parking brake. The aircraft rolled forward then the pilot applied the brakes manually. The aircraft was connected to a tug to reposition and no damage or injury occurred.

Narrative

Parking on ramp spot at ZZZ. We arrived into the parking spot and stopped the aircraft when indicated by the docking system. I set the parking brake; then looked up; and the aircraft began rolling forward. I do not know when the brake released. I put my feet back on the rudder pedals; pushed the brakes; and shut down the engines. The aircraft rolled about 2-2.5 feet forward. I attempted to reset the parking brake; and it would not latch. I had the First Officer press his brakes; and attempted to set the parking brake; and it would still not latch. The total attempted resets was about 6. We got on the headset with the mechanic; and shared with him the brake would not set; and they chalked the aircraft. We continued with the shutdown checklist; then were hooked up to the tug to be pushed back into position. When the mechanic came on board; we were able to set the parking brake. I do not know if this was because we changed the state of the aircraft via the shutdown checklist. No damage to property or persons occurred.