NO it's not a habit from me.

Thnx Jasper Kalkman.

plugins/filters/setup.php

@@ -25,7 +25,7 @@
  */
 
 /* Path for SquirrelMail required files. */
-if (!defined('SM_PATH') define('SM_PATH','../../');
+if (!defined('SM_PATH')) define('SM_PATH','../../');
 /* SquirrelMail required files. */
 require_once(SM_PATH . 'plugins/filters/filters.php');