Minor Nocturne Q Visual Glitch

I've noticed this bug for a while, and although it's very minor, it's still annoying. After casting Nocturne's Q, sometimes when auto-attacking, the button will flash, as though it's cooldown is being reduced (such as Yi's Q when he auto-attacks). IF you watch the linked video, while he's attacking gromp it does it a couple of times and even points it out. I think just the passive is supposed to blink, not the Q.