Conqueror doesn't proc on Damage over Time properly

I was thinking of trying Conqueror on Brand since when he's fighting his dot can last on a target for a long time. I know about the hotfix shortening the length it lasts on ranged champs, but was that hotfix also meant to make it so Damage over Time doesn't work with conqueror right? I tested it with Cassiopia, Brand and Malzahar and none of their DoT spells refresh the stacks like I thought they were supposed to. I think it is still applying a stack if the DoT lasts more than 5 seconds, but they fall off after 2 seconds even while the DoT is still active (Brand's burn is 4 seconds long, so I had hoped that would let me space my spells and keep Conqueror going for longer).

Was this intentional or is it a bug and the rune is supposed to still work with Damage over Time spells?