[Excaliber]

I see what you mean. While the drive would freewheel for a while, eventually it would tend to 'seize up' due to heat or just plain mechanical failure and then could damage the starter motor itself.

Now the starter WILL NOT spin until the drive is fully extended. If the drive CANNOT be fully extended because the shaft or the drive has been damaged the starter won't spin. The starter shaft is the tip of the starter armature, if the shaft is damaged, the starter is effectivly ruined.

While you might be able to pull the drive out manually (your fingers or pliers or something) being PUSHED out by the starter is different thing. Unless the shaft is nice and smooth it could easily hang up 'half way' there. That would explain why sometimes the starter works (out of the car) and sometimes it doesn't. I bet the drive is NOT fully extending.