I was refused a seat despite having a re-confirmed return leg for LH flight from HCMC(Saigon) to Bangkok on 21.Nov. 2010. If you had a similar experience you may want to send an official complaint, to Luftfahrt-Bundesamt
http://www.lba.de regarding infringement of air/passenger regulations. As for me, I will never book a Lufthansa (and due to poor previous experiences I may add Air France) flight – the concept of customer care seems frightening and alien to this company. Posted by a frequent (800+ flights so far) flyer.