Of course, I had the blueprints saved in my blueprints... and since then I've deleted the books.
If there's a way to get them back I'd gladly try to retrieve them again, but as it stands I can't replicate the bug anymore.

I was making a blueprint book with some useful train blueprints to work in conjunction with a book I found online While doing so, suddenly when shift-scrolling through my book it didn't switch the blueprints (though the names changed), any other blueprint book worked fine, and even if I made a copy ...