It is not a bug, stand alone armor (the ones you cannot add arms and legs to) are not available to the Qunari. Kind of makes sense.. there are no Qunari in the Orlesian army, there are no Qunari wardens, no Qunari seekers until now, etc etc etc.
Okay, so confirmed that standalone armor like Templar Armor and Warden Armor is race-restricted and Qunari can't wear them? Or can they wear them but nothing unique renders?
The specific bug we're talking about is when Qunari characters equip universally available armor (armor which isn't race-restricted) like, for example, the Inquisitor Armor sets (Inquisitor Foot Soldier for Warriors, Inquisitor Scout Armor for Rogues, and Inquisitor Battlemage Armor for Mages). When I equipped my Qunari warrior with the Inquisitor Foot Soldier armor (which is available to Qunari characters), it doesn't render ANYTHING resembling armor.
What it renders/equips is the pyjamas.
So... yeah. It's a bug. Unless you believe Inquisitor Foot Soldier armor, which appears as plate armor on all companions and other Inquisitor races, should look like pyjamas on a Qunari.