Can you help with my iPhone syncing issue?

When I listen to podcasts on my iPhone then sync it with iTunes, for some reason iTunes is not recognizing that those episodes aren’t new. This also happens the other way around when I mark them as “not new” on iTunes, it doesn’t register on my iPhone. This is annoying me because I listen to quite a few podcasts and don’t want to have to sift through them to figure out what I’ve heard and what I haven’t.

Any ideas on what’s happening?