Ideally, as a result of the post-mortem, the same mistake shouldn't even be repeatable, because mechanisms should be introduced to prevent it. And if someone k

Ideally, as a result of the post-mortem, the same mistake shouldn't even be repeatable, because mechanisms should be introduced to prevent it. And if someone keeps making new original mistakes, revealing vulnerabilities in your processes, I would say that it is a very valuable employee, a lucky pen-tester of sorts.