thank you Austman - you confirm my own experiences. I learned, that if I wouldn't learn the rules (and some ways around them), it wouldn't work as smooth as I want it.
Under "Ansett" you see some postings helping me over a "booking-class" problem yesterday - our "downunder"-colleagues on FlyerTalk did solve the problem for me (at least that's what I hope - no confirmation yet from LH).
Here an unpublished rule in add: I/you can't upgrade (using vouchers or miles) paid RTW UA-business-class "D" to first outside US/Canada/Mexico - but you can upgrade bus-first on LH-segments.