I was partway through a Kill the Trolls quest and got distracted by other pressing matters. Before I could go back and complete the quest, a new monster lair spawned on top of the quest collection square. I killed the monsters and looted their lair, but the quest is now a zombie, unable to be completed and still listed as active with leftover artifacts lingering on the map. Seems like freshly spawning in events that would ruin an already open event present in the square should either A) not spawn in there, or tidy things up after stomping on the open event. I vote for A).

Speaking of quests, I'm going to segway to a [0.86][Enhancement] semi-related topic here in the same thread.

Would it be helpful to offer an Abandon Quest button, like on the active quest page in the ledger? This button would be for voluntary use when you decide to permanently abort a quest that you regret agreeing to do in the first place. Perhaps this is more of an esoteric concern, but at least you'd have a way to declutter the active quests tree on the left side of the main map.