nginx回源使用localhost产生问题

最近测试ngx_http_slice模块，回源的时候填的localhost结果老是超时，还以为是slice模块有问题，后来无意间改成127.0.0.1后就没有问题了 真是见鬼了

#user  root;
worker_processes  1;
events {
    worker_connections  1024;
}
http {
    include       mime.types;
    default_type  application/octet-stream;
    proxy_cache_path d:/cache levels=1:2 keys_zone=cache_one:100m max_size=1g inactive=30m use_temp_path=off;
    log_format  testfmt  '$remote_addr - $remote_user [$time_local] "$request" '
            '$status $sent_http_content_range $body_bytes_sent "$http_referer" '
            '"$http_user_agent" "$http_x_forwarded_for"';
    sendfile        on;
    keepalive_timeout  65;
    server {
        listen       38081;
        location / {
            #content_by_lua 'ngx.say("success") ngx.exit(ngx.OK)';
            root   d:/Media;
            index  index.html index.htm;
        }
        access_log 38081.log testfmt;
    }
    server {
        listen       38080;
        location / {
            slice             2m;
            proxy_cache       cache_one;
            proxy_cache_key   $uri$is_args$args$slice_range;
            proxy_set_header  Range $slice_range;
            proxy_cache_valid 200 206 1h;
            proxy_pass        http://127.0.0.1:38081;
            root   webroot;
            index  index.html index.htm;
        }
    }
}