Unwritten book and quills reduce their own page numbers by 3 after closing and opening them again

I got a book and quill from the creative inventory, and clicked "Write". I set it to be 30 pages, then I closed the write screen and opened it again. It showed 27 pages. I did it again with another book and quill, but instead, with 38 pages turning into 35. Pls fix!

https://youtu.be/BgPyGkdLRoE for video