Assassin Kennen and RFC buggy

I just build a Kennen with a RFC and the Assassins spatula. Which doesn't make him jump like an Assassin. He just stands in the back and autoattacks around the map (which nullifies his ult because no enemy is in range :-D). I have to guess that this is a bug, because the jumping to the farthest enemy is an essential part of the Assassins buff, and should not be overwritten by a long attack range?