As a beta tester I am installing upgrades every few weeks and I never have any problems — but then my user and keychain passwords are the same. Specifically what upgrade process did you follow? Have you considered changing your keychain password to match your user password then after updating changing your keychain password back to whatever you want it to be? Certainly not ideal but if it works you could use it as a workaround.
I think I've tried every possible variety of clean install imaginable (plus one uograde), all with the same results.
I tried your workaround weeks ago, and my keychain turned up empty after a restart, but I couldn't even do it when I tried again a few days ago.
I've now got a pretty good handle on what's going on, and I'll post in my "Migration Question" thread after I get my new enclosure from OWC and complete my research.