If you already has cached eggs, there's no error, that's why we're using mkdir eggs && bin/buildout buildout:eggs-directory="eggs" buildout:download-cache="eggs", to force it to always download the eggs.
@mauritsvanrees using the virtualenv and different bootstrap (for buildout 1 and 2) we still get the same error if zc.buildout is pinned to any version different from 2.9.5.