Felbog Fang does not function with Impending Doom

When casting Despair linked to Impending Doom, if the curse duration expires it will deal damage as though the curse is still on the enemy. Despair correctly affects the damage of Impending Doom.

However, if you equip the Felbog Fang, it's damage bonuses do NOT apply, even though the explosion DOES get scaled by the curse that should be at 100% expired, thus should be granting the buffs from Felbog Fang.

So, how did you know that? I found a post (https://www.reddit.com/r/PathOfExileBuilds/comments/zbe1dd/questions_about_impending_doom_and_curse_mechanics/) gave the opposite conclusion.

I have no idea how to test it.

I tested it by checking damage with and without felbog in BA on low damage, was no difference. Tested it with diallas and anomalous impending doom. It might be that the curse is still applied but the felbog fang effect is not.