this:
doesn't seem to work properly. because some applications like 'lxsession-logout', which is very important for logout and shutdown, ignores '--primary' option and displays its stuff on HDMI-0 instead of DVI-0

how to solve it?
thanks.

Which video driver are you using?

I'm not sure, here is some info:

/dev/fb0
/dev/dri/card0
/dev/dri/controlD64

server glx vendor string: SGI
client glx vendor string: Mesa Project and SGI
OpenGL vendor string: X.Org

OpenGL vendor string: X.Org
[ 26.400] (II) LoadModule: "extmod"
[ 26.402] (II) LoadModule: "dbe"
[ 26.402] (II) LoadModule: "glx"
[ 26.405] (II) LoadModule: "record"
[ 26.406] (II) LoadModule: "dri"
[ 26.407] (II) LoadModule: "dri2"
[ 26.407] (II) LoadModule: "ati"
[ 26.408] (II) LoadModule: "radeon"
[ 26.414] (II) LoadModule: "vesa"
[ 26.416] (II) LoadModule: "fbdev"
[ 26.425] (II) LoadModule: "fbdevhw"
[ 26.426] (II) LoadModule: "exa"
[ 26.814] (II) LoadModule: "fb"
[ 26.817] (II) LoadModule: "ramdac"
[ 26.951] (II) LoadModule: "evdev"

It seems you're using an ATI driver. I thought that perhaps you use nvidia binary driver which only just started fully supporting xrandr in beta version but it doesn't seem to be case here.