On Air New Zealand at least, Z is the class given to economy tickets upgraded to business. They have a special fare class for it so as to distinguish it from paid biz tickets for mileage-earning purposes (as far as I know). Not sure if Lufthansa has the same, but it would at least explain some of the things you're seeing.

Cheers, Zac

[This message has been edited by Zaco (edited 10-15-2002).]