Index: wp-admin/includes/bookmark.php
===================================================================
--- wp-admin/includes/bookmark.php	(revision 18535)
+++ wp-admin/includes/bookmark.php	(working copy)
@@ -30,6 +30,10 @@
 		wp_die( __( 'Cheatin’ uh?' ) );
 
 	$_POST['link_url'] = esc_html( $_POST['link_url'] );
+	
+	// Preserve parentheses and square brackets	- see #16859
+	$_POST['link_url'] = str_replace( Array('(',')','[',']'), Array('%28','%29','%5B','%5D'), $_POST['link_url'] );
+	
 	$_POST['link_url'] = esc_url($_POST['link_url']);
 	$_POST['link_name'] = esc_html( $_POST['link_name'] );
 	$_POST['link_image'] = esc_html( $_POST['link_image'] );