The pilot stated that he was preparing to fly the airplane with a new propeller that had been recently installed. During a few recent experiences, the propeller would get stuck at top dead center and would only turn normally after multiple start attempts. On the day of the accident, the propeller was stuck at top dead center again after an unsuccessful attempt to start the engine. The pilot walked to the front of the airplane and stood on one of the floats to reposition the propeller, at which time the engine started up immediately and the pilot was struck by one of the propeller blades. According to the airport manager who arrived several minutes after the accident, he observed the ignition switch in the ON position. The pilot further remarked that he must have forgotten to turn off the magnetos before he moved the propeller. The pilot reported no preimpact mechanical malfunctions or anomalies that could have precluded normal operation.