Introduced in 286b007bd327a1e8d6d1fe66702b951f2fd6e29a and then
in 2e6b796761672e0e3ed685487007bb0d99126d91.
This a proper fix for what 70c6f6572dda0f2516bad812857ef814ec710a12 tried to do.
Removing the "config" prefix triggers the bug on pure nixos too, not only
on nixops.