blackstaff +bludge stacks?

[disastro]

blackstaff adds 1 dice of random elemental damage and 1 dice of +bludgeoning damage. does this bonuse bludgeoning stack with the +bludge damage that is already on the base item? if i recall correctly darkfire/flame weapon damage wont stack onto a weapon that already deals fire damage, is it the same for other damage types?

I tried it out on a crafted magic staff (that already has +bludge on it) and the elemental damage showed up on my character sheet but not the +bludgeoning (rather, the +bludgeoning damage stayed the same).

if, as it appears, this damage doesnt stack then that poses problems for blackstaff since most every staff over level 1 includes some kind of +bludge on it as far as I know. unfortunately i cant think of a good way to test this.