The furniture are stacked in draw order but also to elevation 0.
In real world, even a rug has a high (about 1~2cm).
Try this:
-put a chair (eg.Living room -> Armchair)
-put a rug over chair (eg.Living room -> Oriental rug)=> the rug hide the chair
-from furniture list on the left-bottom panel, select (double-click) the Armchair and modify the elevation from 0 to 1.5cm or 2cm
-verify the accuracy in 2D and 3D.