Bizarre brake situation, how can this happen?

[unpolire]

Recently I gave my 2003 Boxster Tiptronic to an automotive restoration shop that I have used for bodywork in the past. They offer full restoration services, so since I wanted a new top installed and my leather seat bottoms recovered, I also let them install all new brakes and hardware, excluding the calipers, but including the parking brake shoes and hardware. I supplied all of the factory Porsche hardware and sensors along with upgraded black oxide slotted and drilled rotors and carbon ceramic pads. Prior to this the car had been fully serviced by an ex-factory Porsche mechanic who has a thriving shop. He had informed me that my brakes were the originals and I needed the supplied parts replaced.

When I picked up the car from the restorer, I asked if the parking brake was now working and I was assured that the brakes were all working perfectly. I got the car in the evening and drove it home in the dark. I noticed a loud grinding noise coming from the left rear on the drive back, but couldn't stop to analyze it in the dark. The next day I start checking everything and found the front and rear wheels and tires mismounted, with one rear on the left front and the front on the rear! In pulling off the wheels and tires to reposition, I noticed the rotor set screws MISSING from the rotors. Even more alarming was the new groove in the new left rear rotor where it went metal to metal in contact with the rear caliper pin! How could this happen with the wheel clamping the rotor to the hub, even with the set screws missing? Is there something else seriously wrong after they installed the new rotors and parking brake shoes? I'm going to take it all apart but want some guidance as to what could possibly have occurred. The mechanic who did the work has already been fired by the shop as he also didn't close fastners, bleed nipple covers, and the rest of the mistakes.