That's the screen it shows when you first log in on a computer. I'm inclined to think it may be something related to the upgrade then. I wouldn't have the foggiest what it maybe however because its working for me. I can understand your frustration though, I don't care for the mobile site either.
One last suggestion, can you change the skin from the bottom left corner of the screen, even without selecting the full site link? I know I can pick a mobile skin from my computer, maybe you can pick a standard skin.