[Gameplay] Malzahar's Ult does not Disable Kalista's Autoattack

Noticed this bug in a normal game today, don't know if this is a Kalista specific problem or not, but upon using Malzahar's ult to suppress Kalista (who was NOT utilizing any tenacity), Kalista, while unable to move or use abilities, would still autoattack Malzahar. Only noticed it once so far, but it was gamechanging enough (not stopping an ADC from attacking is kind of a big deal) to make a report on it.

(possible) Steps to reproduce:

1. Play Malzahar
2. Hit Level 6
3. Ult a Kalista that is currently autoattacking you

Could also be a possible item interaction, Malzahar build was: Void Staff, Mejai's, Rod of Ages, Deathcap, Sorc Boots, Liandry's Torment. Kalista's build was: Runaan's Hurricane, Bloodthirster, Berserker's Greaves, Negatron Cloak, Blade of the Ruined King, Infinity Edge. Only ulted Kalista 3 times during the match, but was autoattacked for the duration all 3 times.

Match History (in case rito has magical "watch replays of old matches" powers) http://matchhistory.na.leagueoflegends.com/en/#match-details/NA1/1764466879/47362795?tab=stats