Never seen it either, that could have been real bad! It does look thin though. Heating up and applying pressure to a thin piece of cast....I could see that happening.
not your fault whoever turned them last should have miced and then scrapped them I've been forced to buy new drums by brake shops for that reason and mine were 3 or 4 times thicker than those your lucky to be able to show us those
I've seen it too. Recently. It was on the rear of a ford tempo. Fortunately there was a rear hub and bearing there and the drum was just floating between backing plate and the hub. The *** kicker is that there was a rust ring on the back of the drum and I had to crack the drum apart.