disagreed numbskull,
regardless of whether start valve is open or closed, the starter 'disengages' from spooling up engine long before it reaches idle (aircraft engine speed exceeding pawl liftoff speed of starter drive shaft assembly).
as VTM mentioned, since the starter can still be supplied with pneumatics from its own engine, the starter will still continue to motor. the speed at which it continues to operate is determined strictly by the pneumatic pressure, not engine speed.
none the less, because i don't know what effect prolonged motoring might have on the starter and company procedure dictates, i will s/d immediately.
rgds
cod