[jQuery] When adding class parent fieldset my select loses focus

[jQuery] When adding class parent fieldset my select loses focus


I have a form wich uses this js:
$(document).ready(function() {
    $(':input').focus(function() {
        $(this).parents('fieldset').siblings().removeClass('notice');
        $(this).parents('fieldset').addClass('notice');
    });
});
This works fine with normal text inputs but when I clicking on a
select in another fieldset you should see all <options> but that's not
what I see.
What I see is that the <options> show just one milisecond an then they
collapse back when the class is applied to the fieldset. Is this a
known Firefox bug? It's really strange because when is apply the class
not on the fieldset but on the parent div it just works fine.
In safari 3.0 it works fine but in 2.0 the fieldset didn't get that
focus.
Maybe this script is a liitle bit to easy or something?