With my necromancer 50 I'm trying out the various spells. I noticed that the drain mana of the Vacuum 25 - 34 -44 spells is the same. The damage changes, the mana cost also, but the amount of mana that is recovered is always equal to the magic level 25. I have tried both on green, blue, yellow and orange mobs. I think it's a bug to fix (it's almost not good to use the yellow magic liv 34 or red liv 44 to get mana).