Need debugging help

I've spent far too long looking at this and not figuring out why this isn't behaving properly.  Why is this causing my entire page to reload?  It should just hide the form and show the thank-you page. I've run similar code many times on my other instance of Marketo with no problems.  This one is weird though...it does the onSuccess action of hiding the form, the preform-div and showing the postform-div but then moments later the entire page reloads. I thought the return false prevented that.

it.gehealthcare.com/rad-ciet-trucktour-shortform.html

if (window.location.href.search('{{my.Alternate-Page-Name}}') >-1) {

  var formNum = {{my.Alternate-Form}};

  document.getElementById("form-div").innerHTML = document.getElementById("alternateForm-html").innerHTML;

  document.getElementById("preform-div").innerHTML = document.getElementById("alternate-preform-html").innerHTML;

  document.getElementById("postform-div").innerHTML = document.getElementById("alternate-postform-html").innerHTML;

  document.getElementById("headline-div").innerHTML = document.getElementById("alternate-headline-html").innerHTML;

} else {

  var formNum = {{my.Main-Form}};

  document.getElementById("form-div").innerHTML = document.getElementById("mainForm-html").innerHTML;

  document.getElementById("preform-div").innerHTML = document.getElementById("main-preform-html").innerHTML;

  document.getElementById("headline-div").innerHTML = document.getElementById("main-headline-html").innerHTML;

    document.getElementById("postform-div").innerHTML = document.getElementById("postform-html").innerHTML;

}  

document.getElementById("postform-div").style.display = "none";  

  MktoForms2.loadForm("//app-aba.marketo.com", "406-TVZ-560", formNum,

      function(form) {

      form.onSuccess(function(values, followUpUrl) {

        form.getFormElem().hide();

        document.getElementById("preform-div").style.display="none";

        document.getElementById("postform-div").style.display="block";

        });

  return false;

    });