Demolisher - wrong tag or wrong description, no apparent effect

The Demolisher support gem has its description say :
Supports any skill, causing Armour Break it inflicts co be stronger.

But I put it on a quarterstaff with Splinter equipped (Break Armour from Physical Damage 15%), and it should now be 21% Armour Break (15% * (1 + 40%)), but the details of the quarterstaff strike does not update.

Looking for an explanation, I found that the Demolisher support gem does have the Spell tag, which could be the reason why it does not work, but then how could I put it on a quarterstaff?