Hey, do you mean that the defender comes out of the stun and immediately throws special in the middle of the combo? That happens to me. But I can't find a reason why it happens sometimes and not others. I believe it is part of a larger "timing" problem and that it was meant to be activated before the stun.
Or maybe the input lag problem where you see yourself attacking but the system did not receiving your attack input and believing that you have ended your combo, the defender launches a special attack.