[Moo] submit form with 2 submit-Buttons

[BMo]

Hi,

I have a problem when I submit this form with Mootools:

<form name="page_form_main" class="gui_window_windowform"
method="post" action="bla.php">
        <input type="submit" class="back" name="back" value="zuruck">
        <input type="submit" name="weiter" value="weiter">
</form>

JS:

....addEvent('submit', function(e) {
         e.stop();
        this.set('send', {
        method: 'post',
        onComplete: function(response) {
         $('gui_window_contentArea').empty().set('html', response);
        }
        });
this.send();
});


The Problem is, that I get both submit buttons and not only the one I
clicked.
PHP echo:
Array ( [back] => zuruck [weiter] => weiter );

Can you help me please!

Thx.