pedido trava se feito por domínio

Question

Eu tenho um aplicativo em que um usuário pode fazer login usando o github. Quando eu entro, o aplicativo trava por cerca de um minuto. Este é o log

Started GET "/" for 177.97.171.165 at 2013-08-11 15:26:01 +0000
Started GET "/sessions/new" for 177.97.171.165 at 2013-08-11 15:26:03 +0000
Started GET "/auth/github" for 177.97.171.165 at 2013-08-11 15:27:03 +0000
(github) Request phase initiated.
Started GET "/auth/github/callback?code=ade18bb431c9303c6274&state=deaf138aff766c6ec3480a54897ae8bbbe734e0dfe11790d" for 177.97.171.165 at 2013-08-11 15:27:05 +0000
(github) Callback phase initiated.
Started GET "/" for 177.97.171.165 at 2013-08-11 15:28:06 +0000

Na última linha, eu estava logado com sucesso. Se eu acessar o aplicativo usando o IP em vez do domínio, isso não acontece, não há atraso de um minuto na requisição. Alguém viu algo assim?

Estou usando o nginx 1.4.1 no Ubuntu 13.04

minha configuração

nginx.conf

user www-data;
worker_processes 1;
pid /run/nginx.pid;

events {
    worker_connections 768;
    # multi_accept on;
}

http {

    ##
    # Basic Settings
    ##

    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    keepalive_timeout 30s;
    types_hash_max_size 2048;
    # server_tokens off;

    server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    ##
    # Logging Settings
    ##

    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;

    ##
    # Gzip Settings
    ##

    gzip on;
    gzip_disable "msie6";

    # gzip_vary on;
    # gzip_proxied any;
    # gzip_comp_level 6;
    # gzip_buffers 16 8k;
    gzip_http_version 1.1;
    # gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;

    ##
    # nginx-naxsi config
    ##
    # Uncomment it if you installed nginx-naxsi
    ##

    #include /etc/nginx/naxsi_core.rules;

    ##
    # nginx-passenger config
    ##
    # Uncomment it if you installed nginx-passenger
    ##

    #passenger_root /usr;
    #passenger_ruby /usr/bin/ruby;

    ##
    # Virtual Host Configs
    ##

    include /etc/nginx/conf.d/*.conf;
    include /etc/nginx/sites-enabled/*;
}

app.conf

upstream chathub { server 127.0.0.1:49153; }
server {
  listen      80;
  server_name chathub.us;
  location    / {
    proxy_pass  http://chathub;
    proxy_http_version 1.1;
    proxy_set_header Upgrade $http_upgrade;
    proxy_set_header Connection "upgrade";
    proxy_set_header Host $http_host;
    #proxy_pass_header Content-Length;
  }
}

Não sei se deixei meu problema claro ... se alguém precisar de mais informações / arquivos, posso postá-los

Editar
A saída das pesquisas

root@chathub:~# nslookup www.github.com
Server:     8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
Name:   www.github.com
Address: 204.232.175.90

root@chathub:~# nslookup www.google.com
Server:     8.8.8.8
Address:    8.8.8.8#53

Non-authoritative answer:
Name:   www.google.com
Address: 74.125.226.208
Name:   www.google.com
Address: 74.125.226.210
Name:   www.google.com
Address: 74.125.226.211
Name:   www.google.com
Address: 74.125.226.212
Name:   www.google.com
Address: 74.125.226.209