I am having the same problem. Already send a report to supportdos@larian.com using the tool.
Unfortunately, I only have hall of heroes unlocked and am 50 hours into the game (lvl 15) I really hope there will be a hotfix available as loading a savegame to (maybe) fix it will set me like 45 hours back which is unacceptable.
I tried killing zixzax (which is hard at lvl 15) didn't work. I tried killing him in front of other portals, didn't work either. I tried entering hall of heroes and going back to the end of time using the teleporter and all sorts of things to trigger the conversation. Zixzax keeps trolling me.
Hoping someone will figure out a workaround as waiting for an offical fix/reply might take a while.
Cheers,
Rabbit
EDIT
Just got a reply from Larian. It seems I did not run into the same bug as you did. I just ignored the green being on the chair in Hall of Heroes. Got a reply from Larian within a day btw, amazing!
Last edited by runrabbit; 07/07/14 04:31 PM.