j查询对话框表单提交未发布值

>我有一个简单的形式，如下所示：

<form method="post" name="change_pass" id="change_pass" action="change_pass2.php">
    <input type="hidden" id="uid" value="<?php echo $userid ?>">
    <div id="dialog" style="display:none">
        <input type="text" name="pass" id="pass">Password :
        <input type="text" name="conf_pass" id="conf_pass">Confirm Password:
    </div>
</form>
<div id="weak" style="display:none" title="Weak password">
    <p >Please make sure your password is atleast 8 characters</p>
</div>
<div id="mismatch" style="display:none" title="Failure">
    <p>Password mismatch</p>
</div>
</body>
</html>

我正在使用jquery ui的对话框函数来创建这样的对话框表单，

$(function(){
    $('#dialog').dialog({
        title : 'You must change your password',
        modal : true,
        closeOnEscape: false,
        dialogClass: 'no-close',
        resizable: false,
        draggable: false,
        buttons: {
            'Change Password' : function() {
                if ( $('#pass').val().length <  8 || $('#pass').val() == 'dantours')  {                         
                    $('#weak').dialog();
                }
                else if ( $('#pass').val() != $('#conf_pass').val()){
                    $('#mismatch').dialog();
                }
                else 
                    $('#change_pass').submit();
                }
        }
    }); 
});

但在change_pass2.php页面上，$_POST 数组是空的。我一直在把头靠在显示器上，试图弄清楚这一点。