Comment # 7 on bug 1186365 from Andrei Borzenkov

(In reply to Fabian Vogt from comment #5)
> Sounds like the display manager (or maybe X itself) selects the wrong VT.

1. If I disable auto-login I get lightdm greeter, I enter my user name and
password and then I get blank screen (while session is completely launched).

2. I installed GNOME/X11 and if I select gnome X11 session in lightdm, I get
normal fully functional GNOME desktop.

3. I still get blank screen if I log out of GNOME and log in into Xfce again.

So it is really Xfce issue and it looks like some OpenGL/HW
acceleration/whatever is missing in Xfce. But I am not familiar with it deep
enough to even start digging. If anyone has any idea where to look ...