A bug in Apple's AV Foundation framework, which handles streaming audio and other media for podcast apps, radio apps, and more, could be behind the mysterious, maddening cellular data spikes many users, myself included, have experienced since updating to iOS 6 or the iPhone 5. In essence, iOS just keeps on downloading data, over and over and over and over again, sometimes gigabytes worth at a time. Here's what PRX Labs found after doing some research into it:
The player appears to get into a state where it makes multiple requests per second and closes them rapidly. Because the ranges of these requests seem to overlap and the requests themselves each carry some overhead, this causes a single download of an MP3 to use significantly more bandwidth than in iOS 5. In one case, the playback of a single 30MB episode caused the transfer of over 100MB of data.
PRX was testing Wi-Fi, but seem to believe cellular, including LTE, would exhibit the same bad behavior. PRX also believes the bug is fixed in iOS 6.0.1, though Matthew Panzarino of The Next Web points out that some believe they're still seeing the bug even after updating.
iMore has had complaints about video podcasts taking longer to download than usual as well, and while it's unknown if the issues are related, it's also impossible to rule them out.
Let's be clear though, this is an issue that is costing real people real money. I've never before gotten close to my $35/6GB data plan limit before, yet last month I blew past it far enough to be surcharged $50. All I do is stream audio, and I haven't been streaming anything different than I used it. Less in fact.
If this isn't fixed already, it needs to be fixed immediately.