When a fighter is stunned, they're not supposed to be able to perform any actions. I've noticed that every time when I try to throw a stunned enemy, they somehow could break from my throw. As you can see in the screenshot above, Cerebella broke through my Parasoul's throw and staggered her, despite being still stunned by Motor Brigade. I can't confirm if this only happens with AI or if players can also use throw break while stunned (since no enemy has ever tried to throw me after I got stunned).