how to issue a relative url redirect from nginx?

How can a redirect be configured in nginx to respond to a certain url with a relative redirect to a specific path?

The nginx documentation suggests that this is the default mode for nginx, but in reality if the location being redirected to starts with a / nginx is responding with an absolute url in the Location field.

For local server configuration containing locations:

location = /a {
  return 301 some/path;
}
location = /b {
  return 301 /qwerty;
}

the response Location to a request to /a is:

Location: some/path

and for /b it is:

Location: http://127.0.0.1/qwerty

however, we would like /b to respond with:

Location: /qwerty

The reason we would like to use relative redirects is that we would like to access nginx from different domains and proxies, e.g. in clear in dev or via ssl-terminating load-balancer, and would rather keep things simple by relieving nginx of needing to understand that context.

FYI these examples were tested against nginx versions 1.4.6 and 1.9.6, using curl e.g.:

curl --head http://127.0.0.1/b

nginx header filter always inserts <scheme>://<host> if return uri starts with /.
(see ngx_http_script_return_code() and ngx_http_header_filter() function in nginx source for reference)

So, if client (e.g. google chrome) can accept Location: /qwerty, you can use the following configure:

location = /b {
    return 301 " /qwerty";    # insert space char before "/qwerty"
}

Another solution can generate Location: /qwerty exactly, via lua-nginx-module and add_header directive:

location = /b {
    add_header Location "/qwerty";
    content_by_lua 'ngx.exit(301)';
}

How does this weird configure work?

use ngx.exit to exit with status code with 301, it does not create "Location" header (return directive always create "Location" header, even empty header value)
use add_header to add Location: /qwerty header, it does not insert <scheme>://<host>