Book module has limited child pages

I'm using Drupal 6.2 and have noticed that only 8 child pages are allowed per book. I'm not sure if it's something on my end or it's a feature built into the book.module in D6.

I had to manually re-create all my books when I upgraded from D5 to D6. I hope I don't have to do the same thing when upgrading to D6 to D7.