Sink -- and where to draw the line?

[David Measer]

A tenant texted with a crazy story about how she heard a loud sound and went to the kitchen and the enamel in the sink had spontaneously cracked. It's a enameled cast iron sink. It seemed very odd, but I wanted to ask a few questions:

1-- anyone heard of this? My best guess is that something very hot was placed on the enamel, then maybe cold water put on it. But if anyone has heard of it, I'd love to learn more.

2--more importantly, where do you draw the line? Is this something I need to fix? Or should they fix it? It's not as cut and dry as a broken appliance or roof leak. Doesn't seem like something I ought to be required to fix, but I don't know.

Thanks!