TL;DR: The path constraint won't work incorrectly with Chain scale if the constrained bones are nested AND another constraint triggers an update for those bones (by also constraining them or any of their parents).
For path constraint, as a performance enhancement, all constrained bone lengths are computed before any constrained bones are scaled by Chain scale mode. That scaling is done by adjusting each bone's world transform directly, without the constrained bones inheriting scale from parents that are also constrained bones that Chain scale mode scales. That results in constrained bones that are each scaled as expected, but their "applied local transform" values computed from the world transform DO consider the parent world transform. This makes the applied transform for the nested bones incorrect.
The applied transform stores the local transform that is the result of applying the constraint. It is stored separately from the unconstrained local transform and is used if another constraint is applied. So, if another constraint is applied that causes the bones along the path to be updated using their incorrect applied transform, those bones won't be correct.
