How Submit a HTML form outside iOS WebApp?

i have a webpage with a form that perfectly run as WebApp (iOS 8.x) but compared to others i've the problem that i wish to submit the form OUTSIDE the WebApp! Whatever i do - the result page (an external URL, too) always is shown INSIDE the WebApp window??!

The form has target="_blank" - didn't work! I tried catch it with jquery:

$('#myForm').submit(function(event) {
  if (window.navigator.standalone) {
    event.preventDefault();
    $('#myForm').attr('target', '_blank');
    $('#myForm').submit();
    ...

or with the submit-button: $('#mySubmitButton').click(function(event) { ...

Works fine in mobile Safari or desktop browsers; always opens new tabs/windows there - but nothing i do forced a jump outside the WebApp :(

After reading dozens of articles every idea is welcome now...