ToME: the Tales of Maj'Eyal

I am playing an arcane blade with staff mastery. I noticed that arcane destruction is giving no physical extra damage if the weapon i use is a staff. Bug. feature or wanted? In case of the last 2: there goes another funny character idea to the waste basket

Could it be that without physical base damage there won't be physical extra damage added?

I think what caused by trouble was that arcane destruction reads that it adds physical damage. So i was looking for a physical part when doing staff combat. But the physical damage is added before the convertion to the damage type of the staff used?
So instead adding physical damage better write weapon damage or something similiar? Does berserking adds before converting too? Have to try it.