Index: wp-includes/formatting.php
===================================================================
--- wp-includes/formatting.php	(revision 20950)
+++ wp-includes/formatting.php	(working copy)
@@ -2548,6 +2548,9 @@
 
 	if ( '' == $url )
 		return $url;
+
+	// Encode Square brackets into the allowable form
+	$url = str_replace( array( '[',']' ), array( '%5B','%5D' ), $url );
 	$url = preg_replace('|[^a-z0-9-~+_.?#=!&;,/:%@$\|*\'()\\x80-\\xff]|i', '', $url);
 	$strip = array('%0d', '%0a', '%0D', '%0A');
 	$url = _deep_replace($strip, $url);