The request header contains some POST data. No matter what you do, when you reload the page, the rquest would be sent again.
The simple solution is to redirect to a new (if not the same) page. This pattern is very common in web applications, and is called Post/Redirect/Get. It's typical for all forms to do a POST, then if successful, you should do a redirect.
Try as much as possible to always separate (in different files) your view script (html mostly) from your controller script (business logic and stuff). In this way, you would always post data to a seperate controller script and then redirect back to a view script which when rendered, will contain no POST data in the request header.