When dropping a Book and than try to change only one Page with /entitydata @e[type=Item] {Item:{tag:{pages:[2:"\"hello\""]}}} , it deletes all Pages in the Book and writes on the first one : Hello
MC-91142
Deleting all Pages of a Book when editing one
Resolved
Invalid
0
That's an ability to empty lists, if you want to edit one, you have to specify all tags in that list