Comment # 15 on bug 1207516 from Stefan Dirsch

Hmm. Can you reproduce this issue in installed system when using this
/etc/X11/xorg.conf (which is being used during installation)

Section "Device"
  Identifier "modesetting"
  Driver  "modesetting"
  Option "PreferCloneMode" "true"
  Option "AccelMethod" "none"
EndSection

Section "Screen"
  Identifier "modesetting"
  Device "modesetting"
EndSection

Section "Device"
  Identifier "fbdev"
  Driver  "fbdev"
EndSection

Section "Screen"
  Identifier "fbdev"
  Device "fbdev"
EndSection

Section "Device"
  Identifier "vesa"
  Driver  "vesa"
EndSection

Section "Screen"
  Identifier "vesa"
  Device "vesa"
EndSection

Section "ServerLayout"
  Identifier "Layout"
  Screen  "modesetting"
  Screen  "fbdev"
  Screen  "vesa"
EndSection