Sometimes the GIMP displays what seems like inexplicable behavior. For this reason, Chapters 1 through 5 each have a final section which addresses common problems. They all seem to be grayed out.
Nothing is wrong.
After hours of exhausting work during which I built an image with multiple layers, masks, and paths, I saved my image to a file. However, the next time I opened my image, much of what I did on the image was missing. This is the only format that can save the state of your GIMP image projects. Once a project has been completed you may want to save it in another format such as JPEG, GIF, PNG, etc.