[GAMEPLAY] Anivia's Invisible Q Bug

I have been noticing, as an Anivia main, that her q will sometimes turn invisible. Flash Frost is Anivia's main engaging/disengaging tool, so it apears as a shock when I cast it, I see it dissapear on the first minion it hits, then I see my opponent I was aiming at get stunned for no reason. Not really that game breaking seeing as how I have only seen it happen maybe half a dozen times in 2 months. It just gets annoying timing a stun, when you can't see it. Anyone else notice this bug?