[jQuery] [HELP] Problem in IE (6&7). Can't use two eventhandlers of change in one *.js file

[ardnet]

The code in my drupal module is more like below:

//--------------- start code -----------------//
$('div#select_cat select').change(function(){
                var check_cat = this.value;
});

$('div#select_subcat').change(function(){
                var sub_cat_id = $('#select_subcat select').val();
                alert(sub_cat_id);
});
//--------------- end code -----------------//

With the code above, I can make the alert box come out in FF, OP, and
Safari. But it doesn't works at all in IE (6&7).
Is this a bug in JQuery? Or there's a mistake in my code?
This is supposed to be no problem at all right?

Thanks, before and after.....