Curses not casting properly in some areas

I've found that on some terrain types in maps, curses don't seem to function. I hadn't noticed this during the campaign, but in some areas on endgame maps I'll cast a curse spell and nothing will happen. Mana is still spent and the character animation still plays, but no spell effect and no debuff occurs. It seems to be more common in areas with narrow pathways, such as the Trenches map.