Index: wp-includes/default-widgets.php
===================================================================
--- wp-includes/default-widgets.php	(revision 21819)
+++ wp-includes/default-widgets.php	(working copy)
@@ -675,6 +675,10 @@
 
 		$output .= '<ul id="recentcomments">';
 		if ( $comments ) {
+			// prime cache for associated posts
+			$post_ids = array_unique( wp_list_pluck( $comments, 'comment_post_ID' ) );
+			_prime_post_caches( $post_ids, false, false );
+		
 			foreach ( (array) $comments as $comment) {
 				$output .=  '<li class="recentcomments">' . /* translators: comments widget: 1: comment author, 2: post link */ sprintf(_x('%1$s on %2$s', 'widgets'), get_comment_author_link(), '<a href="' . esc_url( get_comment_link($comment->comment_ID) ) . '">' . get_the_title($comment->comment_post_ID) . '</a>') . '</li>';
 			}