xfce4-panel does not pick up xrandr 1.2 changes

[Andrew Robinson]

I am using xrandr with 1.2 extensions to configure my multiple monitor
support with a laptop and an external monitor. The xfce4-panel does
not pick up the changes though. When I enable a monitor, then go into
configuring the panel, it does not show that there are two monitors.
Also, when I disable a monitor, the panel doesn't correctly position
itself on the remaining monitor. As a result I have to execute:

if pgrep xfce4-panel > /dev/null ; then
  pkill xfce4-panel
  xfce4-panel &
fi

Which is messy to say the least.

Is there a way to tell xfce4-panel to re-configure itself (a kill
signal for example)?

The man page does not show any options for the panel and it doesn't
seem like there is a way to tell it to re-position itself from the
command-line.

Versions:
xfce4-panel 4.4.1-1ubuntu3
xrandr 1:1.2.2-0ubuntu1
libxrandr2 2:1.2.1-1

Hardware:
Dell Latitude D630 (Intel driver)

Example xrandr usage that is reproducing the problem:

# disable the external monitor:
xrandr --output TMDS-1 --off
# enable the external monitor:
xrandr --output TMDS-1 --auto
# move the external monitor above the laptop display:
xrandr --output TMDS-1 --above LVDS

Thanks,
Andrew