Grasp of guthix does not give kill credit or xp

Just like the title says, if you kill something only using grasp of guthix, you get no xp or kill credit.

I was hoping to afk large groups of mobs with it, where grasp of guthix would clear a lot of mobs along side my regular dps, but now that seems very inefficiënt.

Is this intentional or a bug?