Planet CakePHP

I am at a loss. I submit a form via Ajax using

submitForm: function(element) {
    $.post(
        webroot + 'users/settings',
        $('#AJAXform').serialize(),
        function() {
            var option = $('#AJAXform').find('select option:selected');
            $j.current.v.updateField(element, option.text());
            $j.current.v.removeForms();
        }
    );
}

Indeed everything works fine... that is, until I set the debug level to 0.

Then the Ajax request fails. But the strange thing is that via Firebug I can see that I get an error 404 with written

Not Found

Error:
The requested address '/users/profile' was not found on this server.

The problem is that I'm NOT calling the page /users/profile but rather /users/settings (users/profile is the page on which the form is located). And this only happens with the debug level to 0. So I guess it's something related to security.

One may think I'm being blackholed, but the problem is that the Security component is not currently activated; moreover the blackhole should send a blank page, and not an error 404 (even less for the wrong page).

EDIT: I solved it. It turned out it was a redirect in the response which was giving an error. When debug = 0, that error would not be shown and a 404 would appear instead. Firefox would then guess the 404 message (which was not actually sent)