To me, it looks like it has been "picked at" and the aluminium pulled away from the cover and bent, and then won't bend back ... just like when you align one a bit out and try and pull the aluminium off to realign it to find that you can't, and the aluminium just bends badly. I would suspect the customer was a bit too inquisitive on how they are made/put together. You can't tell that to the customer though. Hopefully you just have to replace this one, and they haven't bought a batch and want them all replacing.