Lucian's Q Interaction with Sivir's Spell Shield

The other day I was playing Lucian against Sivir in ranked, and I found that if Sivir activated her spell shield to block Lucian's Q the damage would go through because the initial "wind-up" would proc the spell shield, not the actual spell. Just wondering if any one else has seen this issue, if I used Lucian's Q on a minion the spell shield wouldn't proc and would block the damage, but by using the Q on Sivir directly the damage would go through because of the delay. Is this a bug or intentional?