On April 19, 2003, approximately 1715 Pacific daylight time, a Maule MX-7-235, N114MK, nosed over during the landing roll at a private grass airstrip near Plummer, Idaho. The commercial pilot and his passenger were not injured, but the aircraft, which is owned and operated by the pilot, sustained substantial damage. The 14 CFR Part 91 personal pleasure flight, which departed Saint Maries, Idaho, about 15 minutes earlier, was being operated in visual meteorological conditions. No flight plan was filed. There was no report of an ELT activation. According to the pilot, during the last part of the landing roll, as he was applying the brakes, the left main gear brake locked up, resulting in the tailwheel-equipped aircraft pulling hard to the left. As he tried to bring the aircraft to a stop, it nosed over onto its back. According to the FAA Airworthiness Inspector who responded to the accident site, the parking brake lock activation tab on the left brake master cylinder became stuck on the master cylinder plunger rod, resulting in a situation where the pilot was unable to reduce braking pressure on the left side. A further inspection of the system revealed that there was a burr on the master cylinder shaft. When the left brake was applied and then released, the burr lifted the parking brake locking tab, through which the cylinder shaft passes, and the spring that should press the tab back down to the unlocked position was unable to do so. This resulted in the failure of the brake to release, and it therefore remained locked in whatever had been its most fully-applied position. The FAA Airworthiness Inspector who examined the system after the accident was able to duplicate the malfunction during his inspection (see attached FAA report).