I have encountered this exact problem several times. While the starter is cranking the engine, the torque load of the starter pinion binds the gears together tightly enough that the voltage to the solenoid windings can be removed (turn the key off and remove it) and the starter will continue to crank. It's in enough of a bind that the gears cannot disaengage and allow the solenoid plunger to back away from the button that engages the electrical contacts at the back end of the solenoid. The only way to stop the starter from turning is to disconnect a battery cable. TUNE THE ENGINE SO IT WILL START QUICKLY AND THE PROBLEM WILL GO AWAY. Once the engine fires, the flywheel gets ahead of the starter pinion gear and allows it to disengage.

If you continue to ignore my advice, I will not contribute to this thread any further.
Jerry

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