PowerPress treats the /podcast slug of your WordPress site as the default place for podcasts within WordPress. Because of this, when you use Category Podcasting, it places all episodes you generate into the /podcast slug by default, regardless of any other categories you may have set up. You can try going into the Category Podcasting settings and checking the box next to Strict Categories and clicking the Save Changes button. I'm not sure if this'll help with the /podcast category but it's worth a try.