CLyde, Alex Thank you so much for your replies.
My server is Apache.
I've tried the fix but it doesn't solve the problem. Still on submit the page just refreshes with the defaults filled in.
I was thinking if its to do with the HTTP_POST_VARS in /includes/modules/pages/testimonials_add/header_php.php but in the fix it appears to have changed to _GET but still no success. I'm running php5. Should we be using _POST?