Sorry if I'm necroing here, but I think I might have an idea as to why it's doing that with the wallpaper. When you go through the menu to change the wallpaper, are you choosing to navigate to the picture with a downloaded file manager? Because I had this exact problem and it turned out that it would set the wallpaper fine if I did it using the default Photos app rather than the file manager app I downloaded. Don't know why, possibly because the downloaded app doesn't have as extensive control over the system when activated by another app or something? Anyways I'm hoping that clears it up for you, if you're having the same issue I was.