Edited Issue: Background doesn't render properly with Multiple ModalPopupExtenders [27101]

I have a problem with version 51116 (Nov 2011 release) of the toolkit. When opening multiple ModalPopups, the second ModalPopup that gets opened doesn't get its background rendered properly: it stays behind the first ModalPopup. The screenshots below shows the difference in rendering between versions 40412 and 51116 of the toolkit. Version 40412 on the left is has its first modal popup covered with the second modal popup's backgroundElement, version 51116 on the right is not. Furthermore, version 51116 allows user interaction the first modal popup, which would not be favorable since data on child popups usually is dependent on the action performed on its parent. I also observed some modalpopups that are not rendered properly (child popups appearing under its parent), but that could be resolved with revised code.

Is this a bug? If it's not, are there any versions between these two that features the nice dropshadow (that I like with 51116) but renders the backgroundElement the same with 40412?