Why would you want to place a book on top of a flipped book? You flip books (at a cost of 2 gold/victory points) in order to advance faster on the book keeping track.
Um, I know it's a bit theoretical and not gonna occur often but sometimes you have to put your ink jar on the flipped book. (Suppose that you flipped that book several turns before) But if there's any book you can also achieve at your turn then you might get some rewards from that book.... I guess.
Well it was out of curiosity to be honest. I didn't have chance to feel urged to do that.