Index: wp-admin/edit-attachment-rows.php
===================================================================
--- wp-admin/edit-attachment-rows.php	(revision 7033)
+++ wp-admin/edit-attachment-rows.php	(working copy)
@@ -47,7 +47,7 @@
 	case 'media':
 		?>
 		<td><strong><a href="# TODO: upload.php?action=edit&amp;post=<?php the_ID(); ?>"><?php the_title(); ?></a></strong><br />
-		<?php echo strtoupper(preg_replace('/^.*?\.(\w+)$/', '$1', $post->guid)); ?>
+		<?php echo strtoupper(preg_replace('/^.*?\.(\w+)$/', '$1', get_attached_file($post->ID))); ?>
 		<?php do_action('manage_media_media_column', $post->ID); ?>
 		</td>
 		<?php