I've just had this aswell. I can't make up my mind if this is a bug or not though, It's been a long time since I last played TSL.
I would've presumed that, as there is a certain special weapon in the room, you would only get the one chance, but perhaps it is a bug.
I've tried getting around it with KSE by adding/removing the quest but no luck, the twilek's just won't reappear in the cantina. Oh well, I'm pretty sure we'll eventually get those items elsewhere during the game later on anyway.