Duplicated Leads

Hi, I'm hoping someone can tell me if the following code could be the reason why our form would be firing twice and creating duplicate records in our instance? We implemented this a couple of months back on our BounceX pages. I'm trying to pin down what is causing duplicated leads through these forms. Thanks.

MktoForms2.loadForm("//app-abXX.marketo.com", "XXX-XXX-XXX", XXXX, function(form) {
	form.onSubmit(function(){
		var sEmail = form.vals().Email;
		var chunks = sEmail.split('@');
		var emaildomain = chunks[1];
		form.vals({"Email":sEmail.toLowerCase(),"acbj_emailDomain__c":emaildomain.toLowerCase()});
	});
});‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍