I have been working on a new theme based on a cloned copy of your child theme Photo.
All seemed to work OK, including the background images. Super!
That said, however, problems occurred when I decided that I only wanted the front page to have a background, so I deleted the others images and saved the settings, but nothing changed. The images still showed up in their different locations, yet the images are not shown in the setting page!
All the upload areas where I deleted the image are empty, leaving only the front page image visible.
Is this a BUG or am I doing something wrong?