What gPodder actually does it call playback_from() on the D-Bus interface. This is so that Panucci starts from the position that gPodder thinks is the right one (e.g. if you have listened to the podcast a bit on your computer, it will sync the updated position over gpodder.net and tell Panucci to playback from that position). The code part where this is done can be found by searching for "if player == 'panucci':" in gui.py in gPodder.