Items hide dungeon features for out-of-sight 'l'ook
If there's an item lying on a dungeon feature (stairs, altar, trap, etc), using 'l'ook from out-of-sight to recall that square will only show the item. Since the PC can remember the location of the dungeon feature with ':l', 'l'ook should mention the presence of the dungeon feature, just as it does when the square is in sight.