Now I reproduce it 100%.
From a Hardy I do: ssh -X karmic-host gnome-terminal. While the terminal is connected reboot the Karmic host.
Then do ssh -X karmic-host gnome-terminal again.
Workaround (works 100%): On the Karmic host, rm -rf .dbus/session-bus/*, then reboot the Hardy host.
But maybe this failure occurs in other circumstances when this workaround does not apply.
Now I reproduce it 100%. bus/*, then reboot the Hardy host.
From a Hardy I do: ssh -X karmic-host gnome-terminal. While the terminal is connected reboot the Karmic host.
Then do ssh -X karmic-host gnome-terminal again.
Workaround (works 100%): On the Karmic host, rm -rf .dbus/session-
But maybe this failure occurs in other circumstances when this workaround does not apply.