iTunes U keeps syncing stuff with iBooks!

Everytime new content is downloaded via iTunes U (slides, .pdf, etc.) and I sync my iOS devices (iPhone 4S, iPad 2 - everything latest version) they are all auto synced to my iBooks. I have every possible auto-sync feature off (apps, purchases, books, etc.). Any ideas? It's really annoying. If I want the content on my iOS device, I'll manually do it. Some of these slides are huge and take up a lot of storage.

Thanks.