Mordekaiser Ult interactions

I dont know if anyone noticed this, but in a match I just played as Kayn, I ulted a mordekaiser, and when he preceided to ult a teammate of mine, i just got booted out of him doing no damage on exit and left with a recharged ult. Is this a bug or some kind of interaction devs didnt take into consideration. Feel its highly inconsiderate that since Kayn is literally inside of Mordekaiser that even if he ults, you should still be inside when he ults, and can still choose to exit whenever into the normal world, but still do damage after exiting. This kind of interaction is a really weird one to come across and i feel was not thought about at all when Morde ult was designed.