Unable to turn off screen after docking Latitude E7440 to E-Port II docking station

Hi!

I have a Latitude E7740 that runs Ubuntu Xenial (16.04). I dock it to a "Dell EURO2 Advanced E-port II" docking station. 

If I boot it in the docking station, everything works fine, and I find all my two DVI-connected monitors. 

However, if I undock, then put it into the dock again while running, it fails to enable the screens. I'm using a script called autorandr for switching between display modes - it uses xrandr. It tries to run:

xrandr --output DP1-1 --gamma 1.0:1.0:1.0 --mode 1920x1200 --panning 0x0 --pos 0x0 --rate 59.95 --reflect normal --rotate normal --output DP1-2 --gamma 1.0:1.0:1.0 --mode 1920x1200 --panning 0x0 --pos 1920x0 --rate 59.95 --reflect normal --rotate normal

But the X server responds with:

X Error of failed request: BadMatch (invalid parameter attributes)
  Major opcode of failed request: 140 (RANDR)
  Minor opcode of failed request: 21 (RRSetCrtcConfig)
  Serial number of failed request: 48
  Current serial number in output stream: 48

Running this exact command after booting in the dock is doing the right thing, but after undocking then docking, it doesn't work.

Any ideas here? I have updated to the latest BIOS version.

Problem also reported in launchpad with lot's of debug info, here:

bugs.launchpad.net/.../1585884

Autorandr script is here: github.com/.../