[Synchro909]

I agree with what has been said about the motor starting helping to disengage the starter but it should disengage even if the motor doesn't start. How often have we all tried tostart the motor and it didn't start for whatever reason? The starter always disengages afterwards.
The pinion sometimes jams in the ring gear for reasons best known only to itself but I think it would be worth while checking to verify that the starter shaft is not bent.