Index: wp-admin/includes/export.php
===================================================================
--- wp-admin/includes/export.php	(revision 20117)
+++ wp-admin/includes/export.php	(working copy)
@@ -45,6 +45,7 @@
 		if ( ! $ptype->can_export )
 			$args['content'] = 'post';
 
+		$post_types = array( $args['content'] );
 		$where = $wpdb->prepare( "{$wpdb->posts}.post_type = %s", $args['content'] );
 	} else {
 		$post_types = get_post_types( array( 'can_export' => true ) );
@@ -234,11 +235,13 @@
 	 *
 	 * @since 3.1.0
 	 */
-	function wxr_authors_list() {
+	function wxr_authors_list( $post_types ) {
 		global $wpdb;
 
 		$authors = array();
-		$results = $wpdb->get_results( "SELECT DISTINCT post_author FROM $wpdb->posts" );
+		$esses   = array_fill( 0, count($post_types), '%s' );
+		$results = $wpdb->get_results( $wpdb->prepare( "SELECT DISTINCT post_author FROM $wpdb->posts WHERE {$wpdb->posts}.post_type IN (" . implode( ',', $esses ) . ')', $post_types ) );
+
 		foreach ( (array) $results as $result )
 			$authors[] = get_userdata( $result->post_author );
 
@@ -337,7 +340,7 @@
 	<wp:base_site_url><?php echo wxr_site_url(); ?></wp:base_site_url>
 	<wp:base_blog_url><?php bloginfo_rss( 'url' ); ?></wp:base_blog_url>
 
-<?php wxr_authors_list(); ?>
+<?php wxr_authors_list( $post_types ); ?>
 
 <?php foreach ( $cats as $c ) : ?>
 	<wp:category><wp:term_id><?php echo $c->term_id ?></wp:term_id><wp:category_nicename><?php echo $c->slug; ?></wp:category_nicename><wp:category_parent><?php echo $c->parent ? $cats[$c->parent]->slug : ''; ?></wp:category_parent><?php wxr_cat_name( $c ); ?><?php wxr_category_description( $c ); ?></wp:category>