Comment 6 for bug 1003820

That's a bug in unity-2d then, on the login screen if you click on the gear icon next to the password field you have the session, "ubuntu" is unity-3d, "ubuntu 2d" is unity-2d, you might also want to check .xsession-errors, it might just be that it falls back to 2d because your video driver doesn't support 3d correctly