I'm not sure if anyone else has seen this issue but I've first noticed it after I applied the Feb 2013 CU for SharePoint 2010. I have configured a site with global navigation with links under each heading. When I hover the navigation, a white box appears behind the items. When I scroll up or down, the white box scrolls down with the page and covers other items, almost as if it's z-index is higher than any other item. I've only seen this issue with IE and have been unable to debug it using IE Toolbar since it only appears when I hover over an item. I've tried adding all the classes that are added via css when I hover over an item, but that does not make the whitebox appear and the nav appears correctly. Has anyone else seen this issue? If not, what would be the best way to go about debugging this?
There's an iframe being added to the DOM dynamically. Just add this style to hide it: