Index: wp-includes/canonical.php
===================================================================
--- wp-includes/canonical.php	(revision 19955)
+++ wp-includes/canonical.php	(working copy)
@@ -96,6 +96,11 @@
 			$redirect_url = redirect_guess_404_permalink( $requested_url );
 
 	} elseif ( is_object($wp_rewrite) && $wp_rewrite->using_permalinks() ) {
+		// make sure attachments have the right parent, see #19918
+		if( is_attachment() && ! $redirect_url  ) {
+			$redirect_url = get_attachment_link( get_query_var( 'attachment_id' ) );
+		}
+		
 		// rewriting of old ?p=X, ?m=2004, ?m=200401, ?m=20040101
 		if ( is_attachment() && !empty($_GET['attachment_id']) && ! $redirect_url ) {
 			if ( $redirect_url = get_attachment_link(get_query_var('attachment_id')) )