When drawers are mounted on the left hand side, one of the screw holes is missing on the upper drawer slide - outside walls.  Easy drill hole so no big deal.  What is a big deal is the upper slide itself.  Just as the upper drawer falls into place easily, it also falls out just as easily.  If the drawer has anything in it - it falls on the floor.  There is no drawer slide stop to prevent this.  Just a little bit of thought could have prevented this problem.  At least provide a method to fix this.