Something

/* this works */
<select name = "top_filter[]" onchange="this.form.submit()">

==============================
/* but this does not */
<select name = "top_filter[]" onchange="filter">

<script type="text/javascript">
function filter ()
{
    this.document.forms['filter']['isquery'].value = '0';
    this.form.submit();
    return true;
}
</script>