iPhone 4 bug - can't add iTunes U items to a playlist.
I have a new iPhone 4 and it seems to be a bug.
My workaround is to use iTunes to right click, get info, edit (multiple items) and change Options -> Media Kind to "Podcast".
Then my iPhone syncs.
Suddenly when creating a new playlist and I choose "more" -> Podcasts I can add the items with the + sign and they finally stay/save.