Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 18519)
+++ wp-includes/formatting.php	(working copy)
@@ -2246,6 +2246,10 @@
 
 	if ( '' == $url )
 		return $url;
+		
+	// Preserve parentheses and square brackets	- see #16859
+	$url = str_replace( Array('(',')','[',']'), Array('%28','%29','%5B','%5D'), $url );
+	
 	$url = preg_replace('|[^a-z0-9-~+_.?#=!&;,/:%@$\|*\'()\\x80-\\xff]|i', '', $url);
 	$strip = array('%0d', '%0a', '%0D', '%0A');
 	$url = _deep_replace($strip, $url);