I have below 2 questions regarding browser behavior.
After you do a POST request, browsers keep that information in memory in case they can send it again if you refresh the page. In your case you come from a POST request, so the browser will ask you if you want to send the POST data again, and you cant avoid that.
To avoid it you may add action to the form to a different page and process all the data there.
Or you can process the data on the same page and after processing all the data you can redirect to a new page.
hope this helps..