Starter push button sometimes cycles rapidly during startup

[wf971]

When starting from cold and dark, after having pushed the starter button, before the 

 

Repro:

With external power=ON, ship battery=OFF, place HP lever=ON, Starter Master=ON, now click the push start button until approx 1000RPM (or until the engine sequence no longer requires you to hold the button). The button now cycles in and out rapidly while playing the animation sound. It's an unfortunate bug.