[Gameplay] Sivir's Spell Shield doesn't properly block Varus' Q

I was laning against a Varus recently and despite blocking his Q with my E I'd still take damage. It wasn't the full damage but it was enough that I would lose a trade I had no chance of winning with that ludicrous range. I hadn't taken any auto-attacks for the Q to trigger but even if I had the fact that Spell Shield is supposed to block the ability would mean that it wasn't there to proc the stacks.

What do I expect to happen? Spell Shield should block the ability completely and negate all effects that would come from it. It isn't. Sivir already struggles in lane with the changes and this just adds to it.