Adding in a few 503 status codes for common errors in response to this ExpressionEngine bug about errors getting cached by reverse proxies who cache 200 responses: http://expressionengine.com/bug_tracker/bug/17420
diff --git a/system/core/Input.php b/system/core/Input.php
index 7a16e51..3339d97 100755
--- a/system/core/Input.php
+++ b/system/core/Input.php
@@ -592,6 +592,7 @@
 	{
 		if ( ! preg_match('/^[a-z0-9:_\/-]+$/i', $str))
 		{
+			set_status_header(503);
 			exit('Disallowed Key Characters.');
 		}