The icon on the left is the 'My Documents' icon. It's a separate .ico file than the one on the right, which is the 'folder with files in it' icon. I don't know how Windows handles that icon, as I don't see it in imageres.dll.
EDIT: Also, I'm not sure how Windows handles the folder content previews either (e.g. how the icon on the right has the Microsoft Security Essentials icon in its preview).