[qubex]

Following and furthering your logic, what the hell could they have been doing in the codebase to revert a control mechanism that was effective up to and including 10.12.6, but unsafe as of 10.13.0 onwards???

[CiPHPerCoder]

A graceful upgrade mechanism towards a new password hashing algorithm.

[glhaynes]

Change is so, so risky.

[CiPHPerCoder]

There's a lot that can go wrong, which is why writing testable code and then /actually/ testing it, matters so much.