The renderer drew the root node of an opacity mask's art, of placed symbol
art, of an art brush piece, of an Image Trace source image and of a node
thumbnail without its own opacity mask. Make Opacity Mask uses the top
object as the mask art, so a mask made from an object that already had an
opacity mask ignored that inner mask. These roots now draw through the
same masked group as any other node, still drawn whatever their visibility
and bounds, and an incomplete inner mask still leaves out the outer object.