I use the hotkeys to navigate dialogue in NWN, and the hotkey for add to quest and abandon quest can differ from quest to quest. I just abandoned a quest by accident through reflex. It'd be nice if a confirmation dialogue could be added ("Are you sure you want to abandon the quest?") for noobs like me.
Quest in question is A Watery Exploration. Haven't paid attention to see whether other quests actually have that confirmation in their dialogue tree.