Unable to download archive.zip

Hey, I'm unable to download archive.zip from Gitlab-workhorse, getting following error:

curl "http://127.0.0.1:8181/onny/py-feeds.git/repository/archive.zip?ref=master" -v
[...]
< HTTP/1.1 401 Unauthorized
< Cache-Control: no-cache
< Content-Length: 0
< Content-Type: text/plain
< Date: Mon, 11 Apr 2016 09:54:57 GMT
< Status: 401 Unauthorized
< Www-Authenticate: Basic realm=""
< X-Request-Id: d0d01c1a-8472-4f2d-9939-97ebeab47792
< X-Runtime: 0.006774
[...]

Workhorse is running on port 8181. In other cases, Gitlab-Workhorse seems to respond correctly:

onny@onny ~ % git clone https://git.project-insanity.org/onny/py-feeds.git
Cloning into 'py-feeds'...
remote: Counting objects: 421, done.
remote: Compressing objects: 100% (413/413), done.
remote: Total 421 (delta 291), reused 0 (delta 0)
Receiving objects: 100% (421/421), 29.85 MiB | 5.69 MiB/s, done.
Resolving deltas: 100% (291/291), done.
Checking connectivity... done.

This is my Nginx config:

upstream gitlab {
  server unix:/var/lib/gitlab/sockets/gitlab.socket fail_timeout=0;
}
upstream gitlab-workhorse {
  server 127.0.0.1:8181 fail_timeout=0;
}
server {
  server_name .git.project-insanity.org;
  listen 9080;
  client_max_body_size 20m;
  access_log /var/log/nginx/git.project-insanity.org.access.log;
  error_log /var/log/nginx/git.project-insanity.org.log info;
  location / {
    try_files $uri $uri/index.html $uri.html @gitlab;
  }
  location /uploads/ {
    proxy_read_timeout      300;
    proxy_connect_timeout   300;
    proxy_redirect          off;
    proxy_set_header    Host                $http_host;
    proxy_set_header    X-Real-IP           $remote_addr;
    proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
    proxy_set_header    X-Forwarded-Proto   $scheme;
    proxy_set_header    X-Frame-Options     SAMEORIGIN;
    proxy_pass http://gitlab;
  }
  location @gitlab {
    proxy_read_timeout      300;
    proxy_connect_timeout   300;
    proxy_redirect          off;
    proxy_set_header    Host                $http_host;
    proxy_set_header    X-Real-IP           $remote_addr;
    proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
    proxy_set_header    X-Forwarded-Proto   $scheme;
    proxy_set_header    X-Frame-Options     SAMEORIGIN;
    proxy_pass http://gitlab;
  }
  location ~ ^/[\w\.-]+/[\w\.-]+/(info/refs|git-upload-pack|git-receive-pack)$ {
    error_page 418 = @gitlab-workhorse;
    return 418;
  }
  location ~ ^/[\w\.-]+/[\w\.-]+/repository/archive {
    error_page 418 = @gitlab-workhorse;
    return 418;
  }
  location ~ ^/api/v3/projects/.*/repository/archive {
    error_page 418 = @gitlab-workhorse;
    return 418;
  }
  location @gitlab-workhorse {
    gzip off;
   proxy_connect_timeout   300;                                                                                                                                                                 [0/19]
    proxy_redirect          off;
    proxy_set_header    Host                $http_host;
    proxy_set_header    X-Real-IP           $remote_addr;
    proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
    proxy_set_header    X-Forwarded-Proto   $scheme;
    proxy_set_header    X-Frame-Options     SAMEORIGIN;
    proxy_pass http://gitlab;
  }
  location @gitlab {
    proxy_read_timeout      300;
    proxy_connect_timeout   300;
    proxy_redirect          off;
    proxy_set_header    Host                $http_host;
    proxy_set_header    X-Real-IP           $remote_addr;
    proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
    proxy_set_header    X-Forwarded-Proto   $scheme;
    proxy_set_header    X-Frame-Options     SAMEORIGIN;
    proxy_pass http://gitlab;
  }
  location ~ ^/[\w\.-]+/[\w\.-]+/(info/refs|git-upload-pack|git-receive-pack)$ {
    error_page 418 = @gitlab-workhorse;
    return 418;
  }
  location ~ ^/[\w\.-]+/[\w\.-]+/repository/archive {
    error_page 418 = @gitlab-workhorse;
    return 418;
  }
  location ~ ^/api/v3/projects/.*/repository/archive {
    error_page 418 = @gitlab-workhorse;
    return 418;
  }
  location @gitlab-workhorse {
    gzip off;
    proxy_read_timeout      300;
    proxy_connect_timeout   300;
    proxy_redirect          off;
    proxy_buffering off;
    proxy_set_header    Host                $http_host;
    proxy_set_header    X-Real-IP           $remote_addr;
    proxy_set_header    X-Forwarded-For     $proxy_add_x_forwarded_for;
    proxy_set_header    X-Forwarded-Proto   $scheme;
    proxy_pass http://gitlab-workhorse;
  }
  location ~ ^/(assets)/ {
    root /usr/share/webapps/gitlab/public;
    gzip_static on; # to serve pre-gzipped version
    expires max;
    add_header Cache-Control public;
  }
  error_page 502 /502.html;
}

Thank you and best regards, Jonas