EDIT: Marco beat me to it.

That's a limitation of using stencil shadows. Geometry doesn't clip the shadow, so although it will look nice and pretty on floor one, that same shadow will essentially bleed down to the ground floor. One of a handful of ways to eliminate this and still use your current setup is to turn the furniture model invisible when the player reaches a certain disntance from it.

Code:

---

while(1)

{

   if(vec_dist(my.x,player.x) >= ????)

   {  

      my.invisible = on;

   }

   else

   {

      my.invisible = off;

   }

  wait(1);

}

---

Alternatively, instead of using vec_dist, if the player's X falls outside a certain hardcoded area(like below the 1st floor Z), then you could turn it off that way as well.