Okay, thank you for the additional details. That clarification was helpful. I will try to see if I can reproduce the issue, and if I can find some way to fix it so it works like it's supposed to. I apologize for the inconvenience but I appreciate that you've let me know this is happening. I don't think I'll be able to resolve it for your particular save file though unfortunately.
So in the meanwhile you may wish to start a new file and just get to that point of the mansion again, but get both curiosities before engaging with the encounter this time, and it should proceed like it normally was supposed to. There's no grand reward for collecting every page or anything like that, so you don't have to worry that you missed out on anything terribly important in your original file. On the plus side, once you've already experienced the game, subsequent playthroughs go much more quickly when you already know what to do.