Under Preferences > Store > Automatic Downloads, if I uncheck Music, Apps and Books (the only boxes that are ticked) and close the Preferences window, those items are re-checked the next time I open Preferences. I've tried deleting the com.apple.itunes.plist file, and both the localstorage files that were present in ~/Library/iTunes. I opened the com.apple.itunes.plist file in Xcode, and after examination could find no Boolean that related to Automatic Downloads. The file is definitely user-writeable. I have an active internet connection when I attempt the changes. Advice would be appreciated.