Mike,
sorry for the inconvenience.
Workaround: "killall x2gocleansessions" from another terminal
Solution: Upgrade 4.0.1.14 to 4.0.1.15 (which should be available by now)
A cycle of "apt-get update && apt-get dist-upgrade -y" installed 4.0.1.15 without a hitch.
Logging out of the existing x2go session and logging back in cleared up the keyboard mapping as well.
Many thanks!
—Andreas