I've got the same problem but with videofiles. The only difference I could find is that the video metadata referencing the kind of file (not the media kind) shows up in a different language. eg: "MPEG-4 video file" and "MPEG-4-videobestand". You might want to check if this is the case with your podcasts. If so, this is a very serious bug in my opinion. I have already submitted a bug report to apple. If we all do the same hopefully they'll fix it. This is in Itunes 11.1.1 by the way.
With iTunes 126.96.36.199, I had the same problem with an audiobook. It was just the first one I found, so there are probably more in my library. I solved it by deleting the tracks in iTunes without deleting them from my computer's drive. I then added them back into my library. With music I think that's all you have to do, but with audiobooks you need to change the Media Kind back to "Audiobook" under Options (from Get Info).