Why do podcasts only play 90% when downloaded during 3G on iphone

I've had this problem many times now. When iphone is in contact with wifi, my podcasts on Apple Podcast app and Podcruncher both play 100% of a podcast. But when I'm out and about, my phone will download a podcast but, for example, the 57 minute podcast will reset itself and says its only 44 minutes long. Many podcasts I've downloaded while in 3G (npr, bbc, cbc) all reset themselves once downloaded, on both of my podcast players, playing only 90% of the podcast and the total time shrinks with it too. What is happening?