Actually use the fieldset that's defined.

includes/add_datastream.form.inc

@@ -40,7 +40,6 @@ function islandora_add_datastream_form(array $form, array &$form_state, Abstract
       'dsid' => array(
         '#title' => 'Datastream ID',
         '#description' => t("An ID for this stream that is unique to this object. Must start with a letter and contain only alphanumeric characters, dashes and underscores. The following datastreams are defined by this content model but don't currently exist: <b>@unused_dsids</b>.", array('@unused_dsids' => $unused_datastreams)),
-      ),
         '#type' => 'textfield',
         '#size' => 64,
         '#maxlength' => 64,
@@ -79,6 +78,7 @@ function islandora_add_datastream_form(array $form, array &$form_state, Abstract
         '#type' => 'submit',
         '#value' => t('Add Datastream'),
       ),
+    ),
   );
 }
 
@@ -148,7 +148,7 @@ function islandora_add_datastream_form_field_does_not_contain_a_forward_slash(ar
 }
 
 /**
- * Checks if the given datastream requires the upload to be a certian MIME type.
+ * Checks if the given datastream requires the upload to be a certain MIME type.
  *
  * @param array $form
  *   The Drupal form.