Deliberation damage not calculated on Last Lament's Requiem Skill

I don't know whether it's just a tooltip bug or it's not adding damage at all, but slotting Deliberation (which is one of the recommended support gems) into The Last Lament's Requiem skill does not change the tooltip damage at all. I know there are various supports in the game that don't adjust the tooltip damage, but this support gem DOES change the tooltip damage in every other skill. So, something weird is going on here...