Cassiopea can Ult herself out of Malzahar's ult and it costs me games!

Its basicly just a bug i think or there is something im not getting. If i use my Ult with malza first she just ult's me and thats the end of me and my team! My firend Dugli from EU/NE lost his promo game because of this bug. And if you could arrange a date for my other firend nemaramajvarja EU/NE with Mithy that would be smashing!