The fun thing is I can't reproduce this error now on my development machine (Mac OS). I have the same packages installed, all the same versions.
The site where I experienced the problem is running on Ubuntu 16.04, using a customization of the ansible playbook for Plone. I'll try the same buildout I have on my local machine on the remote server in the next days to see if there is a difference. Maybe a system package in a different version causing a different transformation, as @dieter already mentioned.