No, sorry, doesn’t work. Hovering the mouse over the shopping bag icon in the header, shows a strange behavior. The entire shopping bag ‘pops up’ on top of the screen (as it is supposed to do), but then the product image underneath the shopping bag ‘pushes’ the shopping bag to a ‘lower level’ and the product image then shows on the upper layer. Maybe this has nothing to do with z-index, but with the Product Overlay Transition effect (which I turned off by the way).
When I turn on the Product Overlay Transition effect, and hover a product image, the product featured image will appear. And here we go: when moving away the mouse pointer, the ‘original’ product image will of course re-appear, but when quickly moving the mouse over the shopping bag icon in the header (during the transition effect), the shopping bag IS on top of the page.
So, probably the (Javascript?) Product Overlay Transition causes this shopping bag behavior. Disabling the Product Overlay Transition effect does not solve this problem, but that is probably because the effect script is loaded anyway?