This is because there is a bug where when you disenchant an item, it keeps an NBT tag when its supposed to remove it, therefore causing the disenchanted book to not be able to stack with books that have never been enchanted. There is already an open bug report MC-148476 that shows this.
This is because there is a bug where when you disenchant an item, it keeps an NBT tag when its supposed to remove it, therefore causing the disenchanted book to not be able to stack with books that have never been enchanted. There is already an open bug report MC-148476 that shows this.