--- mailchimp.module.orig	2012-04-18 19:51:20.000000000 -0500
+++ mailchimp.module	2013-01-23 16:47:21.547199696 -0600
@@ -247,7 +247,7 @@
     if (variable_get('mailchimp_interest_groups_user_forms', FALSE)) {
       $interests = _mailchimp_interest_groups_element($q, $list->id, $member_interests, $is_subscribed);
       if (!empty($interests)) {
-        $form['wrapper'. $list->id] = array_merge($form['wrapper'. $list->id], $interests);
+          $form['wrapper'. $list->id] = array_merge($form['wrapper'. $list->id], $interests);
     
         drupal_add_js('Drupal.behaviors.mailchimp = function(context) {
           $(".mailchimp-newsletter-checkbox-'. $list->id .'").click(function(){
@@ -698,9 +698,14 @@
           '#type' => $field_type,
           '#title' => t('@name', array('@name' => $group['name'])),
           '#multiple' => FALSE,
-          '#options' => $options,
-          '#default_value' => $default,
+          '#options' => $options
         );
+        // adding an empty default value causes form api to generate
+        // php warnings by passing an array to check_plain
+        if (!empty($default)) {
+            $element['interest_groups_' . $list_id][$group['id']]['#default_value'] = $default;
+            
+        }
       }
     }
   }