Minor Javadoc improvement.

core/src/main/java/org/springframework/security/ui/AbstractProcessingFilter.java

@@ -122,7 +122,8 @@ import javax.servlet.http.HttpSession;
  * The behaviour is turned off by default. Additionally there is a property <tt>migrateInvalidatedSessionAttributes</tt>
  * which tells if on session invalidation we are to migrate all session attributes from the old session to a newly
  * created one. This is turned on by default, but not used unless <tt>invalidateSessionOnSuccessfulAuthentication</tt>
- * is true.
+ * is true. If you are using this feature in combination with concurrent session control, you should set the
+ * <tt>sessionRegistry</tt> property to make sure that the session information is updated consistently.
  *
  * @author Ben Alex
  * @version $Id$