Images are appearing multiple times and out of order in Book module

[dbe4876]

I have been building a book from a recent vacation to England & France. I ordered all of my images and then began updating the photo text (to use captions). Today, I came back to the Book module and picked up where I'd left off. But, then I noticed my images were out of order, many were in totally strange places. When I look at the filmstrip at the bottom of the window I notice numbers above the images, and hovering over a one of these number I see "Used 2 times in England book." So, it would appear that Lightroom duplicated a lot of my images and stuck them in random places.

Any thoughts on what happened? Why did Lightroom duplicate images in the book and stick them all over the place?