User blog comment:Dragonjet/KC3改/@comment-26168103-20150916040537/@comment-50.132.244.50-20150916044135

See below, that's a symptom of it updating (from 20 to 20.1 in this case) while you were playing. Refreshing the tab should cause quests to properly be removed again when cleared, though ones already cleared that are currently stuck will have to be reset via the Strategy room.