Cassiopeia Heal Bug

There is a bug with Cassiopeia that once I believe when you max your Twin Fang, instead of healing her if the enemy unit is poisoned, other abilities heal her for about 20 health each time she uses it. And it doesn't even have to hit a target. As long as she uses a ability she can heal. It could also be the after I bought Archangel Staff, as it started about it fully upgraded once reached 750 mana.