Adding Photos to a New Book

I've tried to follow the Aperture video tutorial on how to create a book. I select a group of images, and choose, New Book, and then a theme. The blank book template appears, and I can drag images to the book. However, it seems that in my case, the image is actually dragged to the book, and removed from the browser. Is this right? I don't see a badge with a number telling me how many times the picture is used in the book. The image is no longer in the browser at all. I'm a little confused. It's not like the video. Anyone understand this?

Thanks!