The Plaguebringer passive skill "Toxic Emanations" does not benefit from the Cabalist passives "Insidious Decay" and "Power of the First Men".

Repro Steps:
1. Create a character and proceed to level up to ~ level 20.
2. Acquire the Cabalist passives "Insidious Decay" and "Power of the First Men" and the Plaguebringer passive skill "Toxic Emanations".
3. Note the damage number for a single stack of poison ailement on the character's advance detail tab.
4. Proceed to gameplay and stand next to an enemy.
5. Note that the enemy receives only a single stack of ailement every 2 second, making it impossible to quickly stack poison ailement and that it is never multiplied per the "Power of the first men" passive.

Hope this help and that it may be fixed soon,
Cheers

Bob