I ran a quick test myself tonight on jackpot (XI) roll. Naked, I had 162 defense, and idle I had 369 defense before the roll. After the roll, I had 194 naked and 442 in idle gear, which is the expected values for a 20% boost in defense. So it seems to me that it's working as intended.

That being said, why does PLD roll give less defense than DRK roll gives attack?