nginx on Windows always return text/plain

I'm using nginx 1.6.2 on Windows (development machine) and I have an issue where it will always return a text/plain value for the Content-Type header of any file. This is a problem because then browsers won't render CSS, compute JS, etc.

By default I had no default nginx.config file (unlike on Linux) so I had to build it from scratch while keeping it minimal. Normally my issue is solved by including etc/nginx/mime.types so I copy/pasted that file from a CentOS server I have. But it doesn't seem to have any effect. I tried to purposedly make the include path wrong, and that triggered an error, so I think it's actually parsed correctly when I make it correct.

So I have absolutely no idea why nginx keeps returning text/plain for every single fine I have.

This is my nginx.conf file:

events {
  worker_connections  1024;
}

http {
    include     D:/dev/nginx/mime.types;

    expires off;

    default_type application/octet-stream;
    log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                      '$status $body_bytes_sent "$http_referer" '
                      '"$http_user_agent" "$http_x_forwarded_for"';

    access_log  D:/dev/nginx/logs/access.log  main;
    error_log  D:/dev/nginx/logs/error.log;


    upstream backend  {
        server localhost:62755;
    }

    server {
        listen      80;
        server_name localhost;

        client_body_temp_path      D:/dev/nginx/client_body_temp;
        proxy_temp_path            D:/dev/nginx/proxy_temp;


        location / {
            root D:/dev/frontend/src;
            index index.html;
        }

        location /api {
            proxy_pass http://backend;
            proxy_next_upstream error timeout invalid_header http_500 http_502 http_503 http_504;
            proxy_set_header X-Forwarded-For $remote_addr;
            proxy_set_header Host $host;
        }
    }
}