running diablo 3 in virtual desktop

I've gotten Diablo 3 working with wine, but it is only playable inside
a virtual desktop. If I run it outside a virtual desktop, I can't even
get past the login screen and the music stutters.

Inside the virtual desktop, I only get around 10-12 fps. I've found as
infernix on the "Diablo 3" app page has, that if I run wine with the
backbuffer as the render target instead of fbo, it greatly increases
framerate (up to 30-35), but I get the same visual error (his
screenshot below).

tinypic.com/view.php?pic=ay7wcz&s=6

Why would the game only function in a virtual desktop? What's
different about it?  Is there a known performance issue with running
things via fbos instead of the backbuffer?