Archfiends, or at least the chessfiends, technically have maintenance costs, obligatory ones, which cannot be negated nor start chains, thus are mandatory and can result in a loss of duel should they zap your field spell during your Dp and you are forced to pay up during Sp. Maintenance costs, as all costs, are not card effects, hence not negated by skill drain anyhow. The weird part is the interaction between coding probably.