Whilst I'm still working on my book I'm realizing it is going to turn out to have a lot of pages (500+). I'd rather therefore cut it up in episodes and therefore wanted to duplicate the book.

I was able to duplicate it without any issues (File > Duplicate book), however the duplicated version turns out to be quite a different file size (1GB) compared to the original (8,8GB). Did the duplication work properly? Any explanation for this?