掲示板 Forums - Duplicate entries

I know this has been brought up before, but I still don't manage to resolve the issue...
I have merged several word schedules (in my case automated lists from Japanese Basics and Beginner Japanese), but get many "new" terms (with 0 mastery) that I have already learned earlier (in these lists). Recently, these duplicate versions have even started to dominate and start to flood the word lists (and my daily study program).

Is there any way to a) clean the schedule and b) prevent this from happening ?

Thanks a lot !