KitchenAid Artisan Series Mixer pin coming loose?

I have the KSM150PSWM 5 quart mixer but for the last several months (maybe even year) I've had an issue where the pin that holds the motor/top to the base comes loose while mixing. I'm often times having to push it back in or hold it in place.

Is this normal for these mixers? This is my first KitchenAid and I've had it since Feb of 2015. What are your suggestions for correcting this?