SHACO- possible bug with the passive back stab with thunderlords

During my games as shaco I've noticed is that during my fights with enemies on the rift that when i use backstab while chasing them down or any scenerio my thunderlords would not prock. Like for example i would back stab them after Q'ing in and e than back stab again and it would not prock thunderlords and its been an annoyance many times and im hoping a riot employee will see this and make it a priority to fix the bug in a mid patch or next patch so shaco players do not have to struggle with this problem