Guinsoo's Rageblade and Corki [GAMEPLAY]

If you use with it sometimes doesn't activate Guinsoo's Rage. I've narrowed it down to when he kills minions. Basically, from what I perceive while playing, his MAGIC damage (from his auto attacks) occurs FIRST, THEN the PHYSICAL damage, and Guinsoo's Rage is activating off of his Physical Damage. Because of the Magic activating first, if it kills a unit, the Guinsoo's Rage affect doesn't activate.