The other day I just noticed that my iBooks app was missing. Thought maybe I had accidentally deleted it, went to App Store to reinstall and it said the app was already installed. Then I discovered the same thing for Pandora. Very weird. I deleted both and redownloaded - watched while they loaded, then installed. Immediately after installation - poof! - the icon disappears. iTunes shows them as having been installed. I tried a couple of other free apps and they installed just fine. Anybody ever seen or heard of this before, and any clues as to a fix?