Okay, so I've put a full study desk of curiosities on my alt a few days ago and logged today with my main and noticed my alts study desk was full of curios, even though they should have been all used up now.
I logged on my alt, and almost all curios disappeared immediately. So it got back to its normal state, but the problem is it wasn't just a visual bug.
Then I took some of them and put in my main's study report. So I basically used non-existent curios.