My cellular data usage jumped 0.5 GB yesterday morning while I was streaming a video podcast. The podcast was approximately 300 MB. At one point I exited the Podcasts app but resumed streaming the podcast shortly thereafter. (I resumed right where I had paused the stream.)
AT&T shows the data used was 525,032 KB (512 MB), an increase of ⅔ the size of the podcast. (I suspect had I downloaded and not streamed the podcast it would have used less. A little overhead is realistic, but not this much.)
Auto-downloads are disabled.
My next-highest data usage is not even close ―143 MB ― and I have been streaming HD Hulu shows.
This just happened to me last night as well. I told the podcasts app to download some podcasts while I was on my home wifi network. "Use cellular data" was disabled in preferences. I was on my home wifi the entire time, yet when I woke up this morning it had downloaded 200 MB over cellular and I had a data warning. I am deleting this app too, very disappointing.
I thought the whole idea with a podcast player was that you downloaded content to your "pod" (i.e. to an iPhone, via iTunes) and listened to it later. The current podcast player interface is seemingly impossible to setup to allow this type of use without getting messages and/or downloading everything (not just the most recent episodes you haven't heard). Anyone know of a better podcast player? I'd even pay money for it.