Thanks for trying out my game!
As for the sorting minigame, its not a bug because you can swap one book with another so the game will never be blocked. But i am not sure why you mentioned that "it's impossible to take them out again" becauses i just tried to do that and i could pick up the books from the unfinished sections and place them somewhere else. But i suppose it's not obvious that you can swap books, so i will think about how to improve it.
Will try to optimize swiping books for web. Thanks for the heads up :)