Jarvan should not EQ when he is in Cass W

I mean, It is still a movement ability even if it is combo-like! I think amumu should not move either if he lands his Q, he may do damage and stun, but he should not dash! it is like "Grounded prevents ALL movement abilities, well, except this and that and so", why is there always such a laziness when it comes to cass? is it too annoying to make the coding for that? if it were Zed or Annie, it would not be the case....