Vel'Koz Q is not applying the slow.

I was playing Sivir botlane with Lulu against Lucian and Vel'Koz. Whenever Vel'Koz would hit a q on me, it would do the damage and also the visual slow indicator, however my movement speed would not be effected. (I was not using my spellshield). However if he hit Lulu with it it would apply the slow as normal.

TL:DR Vel'Koz Q didnt slow Sivir (without her using spellshield).