Custom post_save() in controller

I’m attempting to follow this guide to extend a module controller so I can override the post_save() function (version 6.5):

I want to call post_save() to customize my return URLs. I have successfully extended the controller, which works, but post_save() isn’t being called and I can’t find anywhere in the code that uses post_save(). Do I need to add a call to post_save() to a specific area or is something wrong?