Index: wp-admin/includes/class-wp-comments-list-table.php
===================================================================
--- wp-admin/includes/class-wp-comments-list-table.php	(revision 17446)
+++ wp-admin/includes/class-wp-comments-list-table.php	(working copy)
@@ -447,7 +447,7 @@
 			$author_url = '';
 		$author_url_display = preg_replace( '|http://(www\.)?|i', '', $author_url );
 		if ( strlen( $author_url_display ) > 50 )
-			$author_url_display = substr( $author_url_display, 0, 49 ) . '...';
+			$author_url_display = wp_html_excerpt( $author_url_display, 49 ) . '…';
 
 		echo "<strong>"; comment_author(); echo '</strong><br />';
 		if ( !empty( $author_url ) )