Just for information as It did surprise me (AY IT does that sometimes.....):
I have a return flight for ZRH-BKK end of November and waitlisted for it with vouchers. Then there was a small flight change which i could not confirm on the web page (gave me errors and i did not have time to inspect this). While being on the website i saw that the flights where shown as waitlisted but hat additional real seat reservations for business class seats. I then wrote an email to confirm the flight changes 4 weeks ago and mentioned this strange behaviour and if they could check. After taking their time they confirmed the change and the business class upgrades for both directions for the LH segments. I'll take it.......
Maybe it helps.... have a nice weekend!