Hidden Fields for MailChimp not always working

Hi Brandon – thanks for a great plug-in.

I’m using MailChimp, and using a hidden field to record where the person signed up. This means if they signed up for a free download, I can send it to them and say “thank you for requesting your free download” etc.

When I test it, it works beautifully. And I’ve seen it work well for others. But sometimes the hidden field is just left blank.

Any ideas how I can fix that?

Many thanks
Shakya.

Site is http://www.briefmindfulness.com,

Hidden field code is

<input type="hidden" value="below single post" name="SIGNEDFROM" class="" id="mce-SIGNEDFROM"><code>or</code><input type="hidden" value="sidebar" name="SIGNEDFROM" class="" id="mce-SIGNEDFROM">

I’m hosted on bluehost, running Genesis with the Sample Theme. eNewsExtended is in the primary sidebar and in a widget area I’ve added on the single post page as follows

// hook this to single post page
add_action('genesis_entry_footer', 'single_post_widget_area'); // this is for HTML5 markup
add_action('genesis_after_post_content', 'single_post_widget_area'); // this is for XHTML
function single_post_widget_area(){
   if(is_single()):
      genesis_widget_area('single-post-widget-area',array(
                          'before'=> '<div class="sp-widget-area widget-area">',
                          'after'=> '</div>')
                         );
   endif;
}

http://wordpress.org/plugins/genesis-enews-extended/