Index: wp-admin/includes/post.php
===================================================================
--- wp-admin/includes/post.php	(revision 25008)
+++ wp-admin/includes/post.php	(working copy)
@@ -61,7 +61,7 @@
 		if (!empty ( $post_data['post_author'] ) ) {
 			$post_data['post_author'] = (int) $post_data['post_author'];
 		} else {
-			$post_data['post_author'] = (int) $post_data['user_ID'];
+			$post_data['post_author'] = (int) get_post( $post_data['ID'] )->post_author;
 		}
 	}