Tabs display problem in IE

The page http://www.live.ba/bs/content/virus-za-symbian-nokia-telefone has a multitab block in the upper right side. When changing tabs, everything looks fine in Firefox, but a click on a tab in IE messes up display (tabs positions moving vertically).

Our Rounded corners configuration is like this:
$("#comments").corner("round 6px");
$(".node").corner("round 6px");
$(".block").corner("round 6px");

Any idea on where to look?

Thanks