Form validation returning FALSE

I'm highly confident that CI does not:

• Change the value of $_SERVER['REQUEST_METHOD']
  
• Put data in the $_POST array when the request method is "GET"
  
• Put data in the $_GET array when the request method is "POST"
  

Have you used your browser's developer tool to examine and confirm the request "type" of the submit?

Here are things I would check

1. Hacked core files
   
2. Extended core classes
   
3. Custom classes / helpers
   
4. Framework Hooks used
   
5. Some javascript weirdness
   
6. Redirect in .htaccess changing a POST to a GET
   
7. Other .htaccess weirdness
   
8. PHP version and/or config
   
9. Server type, version and/or config