This is a relatively minor thing but it's been frustrating. I have a retina MBP running Mountain Lion and it won't keep any wallpaper I set. Every time the computer boots, it's been set back to the "default" wallpaper (the galaxy). When I go into System Prefs -> Desktop, it still shows as though it's set on the wallpaper I selected, but the actual wallpaper on the desktop is always the default galaxy. I reset it back to the one I want, and it's fine until the next time I shut down and reboot, then it's back to the galaxy, every time. Anyone seen this before? If so, does anyone know a simple way to fix it? (Google is failing me.) PS: I did go into the Desktop Pictures folder and I renamed "Galaxy.jpg" and then added a copy of the image I want and titled it "Galaxy.jpg" instead. This "worked", but it's not a genuine fix for the issue, so if anyone can shed any light on how to fix the actual problem, I'd be extremely appreciative!