Cancelling an auto makes the attack reset take the full attack speed cooldown - intermittent

Playing sivir and cancelling my autos because of the screwy game (who hasn't had attackscancelled because of the shitty timings in the game). Some cancelled autos were taking the entire attack-speed cooldown before the next auto started. Others were as instantaneous as if I had just stuttered minorly. I can't believe this game is that retarded.