Menu scenes only have 2 (or 3 if you count the scene background image) object centers (z-index). 0 which is the save game slot thumbnail layer, & 1 which is everything above.
Before 4.x everything used to get drawn below save game thumbnails, but I wanted the option to add images/animations above save game thumbnails so that we could create fancy borders/frames, etc for them. Ideally it would be nice though if there was an additional object center available so that we could draw things below save game thumbnails.