Instacast has hit version 4.2, adding fixes and improvements and a new mode for managing podcast overflow. Turning on News Mode for a podcast marks old episodes as played and deletes any downloaded media once a new episode becomes available. Activate News Mode for a given podcast by going to Settings > Subscriptions, then selecting the desired podcast and activating News Mode.
Other fixes and improvements come with 4.2, as well. The auto-download behavior has been changed to download every new episode, instead of only most recent episode. The mobile data usage setting has been changed. You can choose to not use cellular data at all, don't use cellular to download podcasts, or use cellular data for everything. Fixes have been made to Up Next, episode deletion and reordering, and playback.
You can download Instacast 4.2 from the App Store right now.