The shadow magic spell 'Sand Wurm' which is 4 pips normal and 1 shadow pip (which translates to 4 mana)
Is taking double mana when casting.
Have, say 100 mana, casting this spell should only take 4 away leaving 96. Instead it leaves it at 92, meaning it is double the amount.
Each shadow pip costs the same as the total of the other pips combined. A shadow spell using 5 pips and 1 shadow pip will cost 10 mana; a shadow spell costing 4 pips and a shadow pip will cost 8 mana.