Don't valid private fields on client submission

open.php

@@ -34,7 +34,8 @@ if($_POST):
     if ($topic = Topic::lookup($vars['topicId'])) {
         if ($form = DynamicForm::lookup($topic->ht['form_id'])) {
             $form = $form->instanciate();
-            if (!$form->isValid())
+            // Don't require internal fields (they're not shown)
+            if (!$form->isValid(function($f) { return !$f->get('private'); }))
                 $errors += $form->errors();
         }
     }