missing XINERAMA extension info for dual monitor

[mkt]

I updated a couple of things (kernel and x11) on a centos box running NVIDIA-Linux-x86-173.14.37. Now the window manager just sees one big screen, maximize goes across the two screens and dialog boxes open in the middle. There only seems to be one XINERAMA extension:

xdpyinfo -ext  XINERAMA | grep head
  head #0: 2560x1024 @ 0,0

head #0: 2560x1024 @ 0,0

My screen section is

Section "Screen"
    Identifier     "Screen0"
    Device         "Videocard0"
    Monitor        "Monitor0"
    DefaultDepth    24
    Option         "TwinView" "1"
    Option         "TwinViewXineramaInfoOrder" "CRT-0, CRT-1"
    Option         "metamodes" "CRT-0: nvidia-auto-select +0+0, CRT-1: nvidia-auto-select +1280+0"
    SubSection     "Display"
        Depth       24
    EndSubSection
EndSection

Any ideas?