It might be true though. After the war, the American Air Force took over all the remaining Messerschmitts and flight tested them in the States. There were still a good number of the planes - they never had to fly a mission during the war because of fuel shortage (even the V2 rocket was powered on schnaps in the last stages...). Handbooks have been discovered now, and one chapter describes the handling characteristics of the aeroplane just before AND after breaking the sound barrier. The author has still to be found.