these pages do not match your description of the issue.
in the login page you have sent the redirect is users_LogIn.php?failed=1 not users_LogIn.php?failed=true.
the only way that what you are describing would happen, is if the login form where set to pass any existing querystring variables.
In the login page you sent the action is set to $_SERVER["PHP_SELF"]
<form action="<?php echo ($_SERVER["PHP_SELF"]);?>" method="post" id="WAATKLogInForm">
which wont pass the querystring variables.