Odd thing. This only does it at 20mph? Say I am travelling along on a flat road, motor power only. I get up to 20mph and keep it there for a short while, then reduce the throttle slightly, even though the power meter says that I have reduced power, I am still doing 20mph? Ok, 15 mph reads 3 bars on the meter, 20 mph, 4 bars initially, but after a short while, I can get it down to 3 bars, still doing 20 mph?