Starter not stopping when key returned

[kavadarci]

Hi,
I have experienced a very interesting problem when I start the car sometimes.

It goes like this:
Typically starts on the first turn but
If it’s cold and I need to turn longer for whatever reason until it starts I can return the key to off and the starter is still going.
I can take the key out and the starter is still going.
Once it starts all is well but holly crap if it doesn’t start I need to remove the battery terminal to stop it.

Where do I start with this problem?

I appreciate the feedback.

1976 911 targa, probably original starter.

[john walker's workshop]

Sometimes the starter ring gear teeth are so chewed up that they capture the starter bendix gear and won't let go. Maybe pull the starter and look at the ring gear teeth through the starter hole. In the process, you can see if the bendix gear is wacked, or if it has a return issue. As long as it remains extended, the solenoid contacts are engaged and powering the starter.