Having beaten the Dragonslayer adventure battle for Malakai, I checked the victory conditions tab to see how many I had to complete for the short victory. To my surprise, it showed 5/4, despite me only doing one other battle. Checking my item/ancillary pool, I've noticed that I have two of the Glaive guns (Dreadquake battle reward) and three of the dragonhide cloak (dragonslayer battle reward). As such, I believe the battles are triggering as complete multiple times.