[jQuery] Query z-index problem in IE6 with 1.2.5 and 1.2.6

[Tony]

To reproduce the problem

var aa = jQuey("#content").css('z-index');
var bb = (/^\d+$/.test($("#content").css('z-index')));

1.2.6
FF - aa -> auto; bb -> false
IE6 -aa -> 0 ; bb->true

1.2.3
FF - aa -> auto; bb -> false
IE6 -aa -> undefined ; bb->false

the element
<div id="content">
some content here
</div>

in css there is no attached z-index of this element
Regards
Tony