Grasp of the Undying Bug? Intentional coding? Am I just dumb?

Started playing a few games of top and noticed that my W empowered auto attack does not trigger Grasp of the Undying. Is that intentional?

Also feels like it doesn't always go off, even when it's not on the 4s cooldown. I'm rewatching my twitch stream from last night and it seems like it's pretty hit or miss with the damage going off from the keystone.

Anyone else notice this with other empowered autos? Qs? Am I crazy?