I wonder if it's got something to do with the Causee. As in, that the game doesn't recognize the caster of the arrow (it looked like you used a poison arrow), so it checks the arrow item for the talent and not the caster of it, or something like that.
It's certainly an interesting guess. It would be funny if the AI was looking at the object that applies the status (arrow or grenade in this case), and not the character using the weapon. With that logic, the talent should never work because it's never the actual character applying the status but always a weapon or a spell (unless you fight with bare hands LoL).
