Mail Chimp – Placeholder text for Mailchimp Widget

Hi Guys I know that this issue was discussed previously, however I am still having some issues.
Referring the instruction on the forum http://wordpress.org/support/topic/plugin-mailchimp-list-subscribe-form-request-add-placeholder-text-for-mailchimp-widget?replies=21

I place placeholder=”Your best email….” and I set default merge values in my Form in mail Chimp. When doing it the Fields First Name and Last Name are choosing the values included on the form however, when you click on the field the values don’t disappeared and worst you can submit the form only typing the email address, as the First Name and Last Name are filled with merge values.
How can I fix it?