Fwiw, this bug must have been introduced more recently than Mavericks. I just tested moving my login keychain from one Mavericks computer to another Mavericks computer, and it worked fine. iCloud Keychain disabled on both machines.

Since many if those links are from when Yosemite was current, it wouldn’t surprise me if that was when the bug was introduced. Yosemite made a mess of things in a lot of ways, and Apple has never recovered.