Index: wp-admin/includes/class-wp-media-list-table.php
===================================================================
--- wp-admin/includes/class-wp-media-list-table.php	(revision 20343)
+++ wp-admin/includes/class-wp-media-list-table.php	(working copy)
@@ -130,8 +130,8 @@
 		$posts_columns['icon'] = '';
 		/* translators: column name */
 		$posts_columns['title'] = _x( 'File', 'column name' );
-		$posts_columns['author'] = __( 'Author' );
-		//$posts_columns['tags'] = _x( 'Tags', 'column name' );
+		if ( is_multi_author() )
+			$posts_columns['author'] = __( 'Author' );
 		/* translators: column name */
 		if ( !$this->detached ) {
 			$posts_columns['parent'] = _x( 'Attached to', 'column name' );
Index: wp-admin/includes/class-wp-posts-list-table.php
===================================================================
--- wp-admin/includes/class-wp-posts-list-table.php	(revision 20343)
+++ wp-admin/includes/class-wp-posts-list-table.php	(working copy)
@@ -266,7 +266,7 @@
 		/* translators: manage posts column name */
 		$posts_columns['title'] = _x( 'Title', 'column name' );
 
-		if ( post_type_supports( $post_type, 'author' ) )
+		if ( post_type_supports( $post_type, 'author' ) && is_multi_author() )
 			$posts_columns['author'] = __( 'Author' );
 
 		if ( empty( $post_type ) || is_object_in_taxonomy( $post_type, 'category' ) )