Symfony Form reset after submit - symfony-forms

Question

I have a very simple form created with createFormBuilder providing one simple text field only (there is no entity attached to the form).
When the form is submitted I do some logic and then unset form and formData as suggested in many posts to this topic if you want the form to be reset after submitting.
There is some additional action by simple ajax-requests that mainly initiates some UI stuff - not touching the form itself nor reloading the page.
Everything works fine except that the form apparently just doesn't want to be reset - meaning: Whenever the page reload button in the browser is pressed the standard browser dialog appears that asks if you want to submit the form again. And when you do the last value typed in BEFORE the last render call is submitted.
The template kw.html.twig is straight forward - mainly some UI stuff the form rendering and a bit jquery for handling ajax. Nothing special there.
I can't figure out why this is happening - I just want a clean form on any request. Which I thought I get when unsetting thing like in the sample code below.
/**
* #Route("/kw", name="show_kw")
*/
public function showKwAction(Request $request)
{
if($request->isXmlHttpRequest()) {
if( $request->getMethod() == 'POST' ) {
// do some logic...
return $this->json(array('kw_success' => true));
}
}
$kwData = array();
$kwForm = $this->createFormBuilder($kwData)
->add('kd', TextType::class)
->getForm();
if( $request->isMethod('POST') ) {
$kwForm->handleRequest($request);
$formData = $kwForm->getData();
// do some logic with formData...
unset($kwData);
unset($kwForm);
$kwData = array();
$kwForm = $this->createFormBuilder($kwData)
->add('kd', TextType::class)
->getForm();
}
$templateData = array(
'kwForm' => $kwForm->createView()
);
return $this->render(':backend:kw.html.twig', $templateData);
}
Any help is highly appreciated.
EDIT: Using Symfony 3.1

Answer 1

It's exactly what Alsatian said in the comment. Browser is trying to repeat last request.
However I think that instead of destroying this form you can simply redirect to the same route with $this->redirectToRoute once you processed data, of course if it's not a problem.
Also I see you check at least twice if method is post. If it's not colliding with the rest of your application logic you can specify #Method("POST") in annotation so you don't have to check it directly in code anymore.
Best Regards,
R.