I have one podcast that will not sync to my 5th gen classic iPod. I also have 2 episodes of a different podcast which don't sync as well. They are all video podcasts and have a play count of 0. I normally have my podcasts sync as "all unplayed episodes" for "all" podcasts. I tried to change it to sync "all episodes" of "all podcasts", but they still didn't sync.
The podcasts are: "Aperture 2: Quick Tip" and "D-Town TV | The Weekly Show for Nikon DSLR Users"
If that’s the case, you should be able to convert them by right-clicking or control-clicking and choosing “Create iPod or iPhone Version,” or choosing that from the Advanced menu.