Vader (Duel’s End) FDC Bonus Turns not working properly

The level 15 ability on Vader (Duel’s End) FDC stating that Vader is supposed to gain a bonus turn whenever an enemy attacks out of turn does not grant him any bonus turns. Against Jabba, for example, he does not gain bonus turns when Boushh or anyone else assists, which goes against what the FDC says.