guix pull behind proxy not working

[martin@famic.de]

Hi there!

This is my first contact with Guix System and I managed to install it as
Virtualbox guest system behind a corporate proxy. Well, this was already
quite a challenge and succeeded only due the workaround
(https://guix-devel.gnu.narkive.com/k3oBoFqW/changing-http-proxy-settings-in-guixsd),
but now `guix install` works, I can install new packages (given a
warning about never calling `guix pull`).  However, calling `guix pull`
and `guix system reconfigure` still fails due to unreachable network.
Does it need different proxy settings?  What can I do?

Here is the guix-configuration part of my /etc/config.scm (omitting my
proxy address details):

    (define %my-services
      (modify-services %desktop-services
        (guix-service-type config =>
                           (guix-configuration
                            (inherit config)
                            (http-proxy "http://<IP>:<PORT>")))))

Thanks for any ideas,
Martin