I committed the fix to buildscripts.git and updated buildscripts.git on japsand.x2go.org (which builds & uploads the packages.)
However, for reasons explained in the linked email, I have only rebuilt the "nightly" packages with the key, not the "main" (stable release) packages yet. And the 4.1.0.0 x2goserver nightly package is very unstable.
To any users affected by this bug, I hope to have the main packages rebuilt (and therefore fixed) ASAP.