Morde Q bugged?

I've been playing a lot of Mordekaiser lately and I've noticed when using my Q, as long as the target is walking away, even when slowed by Rylai's, he just sort of chest bumps against them and interrupting his swing until they literally stop moving. Most spells don't work like this, so it feels like a bug for sure. You'd think like most abilities, starting in the range on cast (although in this case they're usually still in auto attack range and I even bought Stinger and had the attack speed mastery) it would continue if they started within range of the ability when it was cast and still do its damage. Still, when I'm watching my champion rub his body up and down their backside, I should still be able to smash, especially with a stinger.