Required Field not required

Hi there,
I’ve setup the Mailchimp signup form which is appearing fine on the website. We are only including the email address field and this is the only one we require customers to enter. In the backend settings the only ‘Merge Variable’ required is the email one, with the Fist Name & Last Names neither required or included in the form.
However, when a customer enters their email address and hits enter they get an error message that says “You must fill in First Name”.
I also suspect if the first name entry issue is fixed then we will have the same issue occur for the last name.
Can you let me know how I can stop this from occuring?
Here’s the website for your reference:
http://www.dineamic.com.au

Thanks,
Simon

https://wordpress.org/plugins/mailchimp/