1999 CV Brake Problem

I heard a metal to metal noise while braking and found the rear passenger side brake pads completely gone. All the other pads were still good. I did notice that on the wheel with the bad pads, the caliper was mounted on the front of the wheel and all the others both front and rear were mounted on the rear of t he wheels. I don't remember ever seeing this before and was wondering if the position of the caliper would cause this pad to wear much faster than the others. I bought this car new and nothing has been changed, so it came from the factory this way. It looks like the same mounting plate was used on both wheels and should not have been. Anyway the brakes lasted 85,000 miles but would have lasted much longer except for the one wheel. I was just wondering if anyone else has noticed this or whether this is a factory screwup. Thanks for comments.