I don't know if it was cheating or a bug, didn't bother checking, but in my last ranked game, I was jungle trundle and enemy had Annie mid. After reaching 4 stacks of her stun early on, she never lost the stacks. No matter what she did, Q, W, Tibbers, only death removed her stacks. And after reaching her 4 stacks again after reviving she had perma stun again. And it was not a visual bug, she literally had perma stun, any ability of hers stunned an enemy.