The pilot of the tailwheel, tundra tire-equipped airplane reported that, before takeoff, while holding short of the runway, he set the parking brake and performed the engine runup. He released the parking brake, taxied onto the runway, and took off for a flight to a nearby airport. The pilot reported that he performed the Before Landing checklist before conducting a short- and soft-field landing on the damp, grass portion of the grass/gravel runway. He added that, about 2 seconds after touchdown, the tail began to lift. He confirmed that his feet were on the floor without actuating the brakes, and he maintained full back elevator control. As the airplane transitioned onto the gravel portion of the runway, the airplane nosed over. The airplane sustained substantial damage to the left wing and empennage. Postaccident examination revealed that the parking brake was partially engaged. The pilot reported that the parking brake system was not damaged, but the system would not return to the "off" position without "jostling the cable." He added that he believed the parking brake system had become "sticky, requiring lubricant." However, given that there was no issue with the parking brake during takeoff, it is unlikely it resulted in the nose-over upon landing.