Removing port from fastcgi redirects

I'm having an issue where some redirects on a website have the proxy-pass port included, rendering them useless. My configuration is as follows:

Physical server 1:

server {
server_name example.com www.example.com;

location / {
proxy_pass http://1.1.1.1:50493;
proxy_set_header X-Real-IP $remote_addr;
proxy_set_header Host "example.com";
}
}



Physical Server 2:

server {
listen 50493;
server_name example.com www.example.com;

set_real_ip_from 1.1.1.1;

root /var/www/example.com;
index index.php index.htm index.html;

location / {
if ($http_host !~ "^example.com"){
set $rule_0 1$rule_0;
}
if ($rule_0 = "1"){
rewrite ^/(.*) http://example.com/$1 permanent;
}
rewrite /[^/]+/([0-9]+)-[^/]+.html http://example.com/showthread.php?t=$1 permanent;
}

location ~ .php$ {
fastcgi_pass 127.0.0.1:9000;
fastcgi_index index.php;
fastcgi_param SCRIPT_FILENAME /var/www/example.com$fastcgi_script_name;
include fastcgi_params;
fastcgi_read_timeout 600s;
fastcgi_buffer_size 512k;
fastcgi_buffers 16 512k;
}
}


Generally, browsing works fine. The site is browsable as one expects. However some links that redirect (eg. after a login action), redirect to a link with the port 50493 included. So we get http://example.com:50493/index.php for example. That will not work. My question is, how do I remove the port in such cases?