Return of Reckoning

For a more techincal explanation. Demon Spittle probobly have the res and armor built in there it as default, but there's a block from those debuffs from happening. Slotting Sweeping Disgorgement probobly just removes this block. Tactics that stacks are probolly seperate effects were they use a skill as the trigger. I'm not a programmer, but thats my guess on why there's the inconsistancy.

Its not a hard coded limitation and is rather an assigned quality. You could easily assign a debuff component of for example demolition strikes to be an ability, tactic, morale, or unique bonus. That is simply up to the person editing the ability.