gentlefury: Not a bug...the first time you beat him you get a choice of prize...the troll head is one of them.
Meleteles Heart is not a main quest...its a side quest. If you screwed up and didn't get the tongue you have the choice to just sell the pendant to the witch.
I think its really cool that your one time decision actually shapes another decision!
It is a bug, because Geralt asks the guy if he can buy the troll head, and he says he'll put it up in a poker match, which of course he doesn't. So either, fix it so he puts it up in the poker game, or remove his response saying he would if you already finished the poker quest.