Index: wp-includes/post-thumbnail-template.php
===================================================================
--- wp-includes/post-thumbnail-template.php	(revision 19664)
+++ wp-includes/post-thumbnail-template.php	(working copy)
@@ -59,12 +59,13 @@
 
 	$thumb_ids = array();
 	foreach ( $wp_query->posts as $post ) {
-		if ( $id = get_post_thumbnail_id( $post->ID ) )
+		if ( ( $id = get_post_thumbnail_id( $post->ID ) ) && ! wp_cache_get( $id, 'posts' ) )
 			$thumb_ids[] = $id;
 	}
 
 	if ( ! empty ( $thumb_ids ) ) {
 		get_posts( array(
+				'cache_results' => true,
 				'update_post_term_cache' => false,
 				'include' => $thumb_ids,
 				'post_type' => 'attachment',