On September 4, 2013, about 1400 central daylight time, N8251K, a Grumman Aircraft Engineering Corporation-Schweizer, G-164B, single engine turboprop airplane, was substantially damaged during landing at Hlavinka Ag Strip, Clemville, Texas. The pilot was not injured. The airplane was registered to and operated by Fehmel Planes, Inc.; Bay City, Texas. Day visual meteorological conditions (VMC) prevailed at the time of the accident and a flight plan had not been filed for the 14 Code of Federal Regulations Part 137 agricultural aircraft application flight. The airplane had departed Hlavinka Ag Strip about 1330 for the local flight. The pilot reported that for several previous several flights his left brake pedal had started to feel "spongy" and that he had to pump the brake pedal while still inflight in order to get adequate brake performance. While inbound for the last landing the pilot again stepped on the brake pedals and the "brakes felt really tight" so he quit applying pressure. During the landing roll, immediately after touchdown, the tail-wheel equipped airplane slowed quickly, nosed over, impacted terrain and came to rest inverted. The impact resulted in substantial damage to the vertical fin, rudder, both upper wings, and the engine mount. A postaccident examination of the parking brake valve revealed loose operation which allowed an uncommanded movement of the valve into the locked position.