Can you post pictures of the pads? When you say "down to the metal" is the friction material completely gone? Are the first and second set from the same source?
The friction material is held to the backing by one or two means. It's bonded on, basically heat causes one material to flow into the structures of the others and when cooled forms shapes that are mechanically interlocked on a microscopic level. The second method improves the first by putting metal rods (usually brass) through the friction material. This increases the bonded area, puts some of the bonding perpendicular to the forces applied and works like a rather poor rivet. Most bike pads are only bonded.
This means that if you bend or twist the pad the whole friction material will eventually fall off. This needs relatively little friction, so you get no heat or smell. I've never seen it on bikes (expertise is on trucks) but imagine an incorrectly sized pin or multiple pistons not working together would give the same result.
A pad that wasn't fully cured would crumble like cake, hence my question about the brand and the supplier.
A disk that is not flat will make a lot of noise and heat in the time it takes to wear away the friction material.