How to delete invisible photos and videos from iPad? MF519LL/A, iOS 8.1.3

General -> About -> Photos = 700 photos

General -> Usage -> Manage Storage -> Photos &amp; Camera = 900 MB

Open Photos app. No photos or videos in any folder (Photos and Albums).

How to clear cache or whatever to free my 900 MB?
Restore it by connecting to a computer with iTunes.  That will fix it.