For my fellow update fanatics information, MadOS MacOS 10.13.3 is — as expected — in beta. No hard information on what it contains, but no new features are expected in this release. I will let you know if I encounter any surprises.
Can't wait! (Really)
It occurred to me that throughout my High Sierra/Keychain Access ordeal I never thought to, nor did anybody ever suggest that I, install via simple upgrade, rather than clean install & migration of data, so I just did an upgrade (on an external volume), and my results were consistent with my previously reported results: my "upgraded" login keychain was
depopulated, and my keychain password no longer differed from my login password.
:shrug:
As I said...Really!
More: I don't think I've ever mentioned that I've run into the same bug with both HFS+ and APFS formatting.