WP7 bug
Podceiver does work over A2DP, but there is a bug in WP7 where sometimes it doesn't expose that output to apps.
My phone once got stuck in this mode, but I was able to get it out eventually. I had the same symptoms as you. A2DP worked fine for built-in Zune and OS sounds, but didn't work for apps.
I'm not sure what fixed it, but here is a list of things I did (in no particular order): unpair/repair the bluetooth, plug-in real headphones to the headphone jack, reboot, turn off, mute/unmute, wait a day. I wish I could tell you the exact steps to fix it, but it just started working again after frustrating me for a few days.