Jquery css opacity - bug in ie8

this

$("ul.main_navigation li:not(.active)").children("ul").css({opacity:0}).addClass("hover");

hides some uls in navigation. It works fine in all browsers (including ie 6 and ie 7), but in ie8 it hides the uls, but not it's content.

The structure:

<ul>
<li><a...></a><开发者_如何转开发;/li>
<ul>

The <a> tags are always visible in ie8...

any ideas? thx