Merge pull request #894 from ravishnair/CRM-12719

-- CRM-12719 applied patch and improved it.

CRM/Case/Form/Activity.php

@@ -617,6 +617,7 @@ class CRM_Case_Form_Activity extends CRM_Activity_Form_Activity {
           $mailStatus = ts("A copy of the activity has also been sent to selected contacts(s).");
         }
         else {
+          $params[$val] = array_flip($params[$val]);
           $this->_relatedContacts = CRM_Activity_BAO_ActivityAssignment::getAssigneeNames($activity->id, TRUE, FALSE);
           $mailStatus .= ' ' . ts("A copy of the activity has also been sent to assignee contacts(s).");
         }