I don't understand. They don't have a prerequisite of the fire being on the ground, so I don't see the comparison. Also, if I've understood it correctly, that's the way D'vorahs non amped bug is supposed to work (go away on hit). In this case, that is clearly not the same as it's not supposed to go away on hit
Maybe the explosion is not supposed to happen on hit. Just like some projectile KBs don't work if you get hit first. We are all just guessing because no one knows if it's a bug or intended.
Have you tested air to air trades? Just an assumption but the extra pushback from the projectile probably goes away if your hit, like the guy said above most attacks lose properties during trades.