I don't really see that as an exception or contradiction, rather a side effect of my poor way of communicating it. This "rule" isn't meant to be exhaustive, but is a mnemonic device for a more complex set of rules that spans one or more pages in a textbook. It works in my head. ;)

The way I see it, a dead person used to be alive before "changing state": in that sense it's a "condition", even if it's not exactly temporary. The difference between ser and estar stems from the inherence of a quality.

I've seen it put in English as: ser is about what something or someone is, estar is used for the how. (You can say: Es un muerto. Because that's what he is. But: Está muerto. He was alive.)

Dato curioso: supuestamente en España se dice "estar casado", en Latinoamerica es "ser casado". Make of that what you will...