[GAMEPLAY] Kalista Ult on Karthus when dead

So I found what i believe is a bug... Kalista was able to ult me, playing karthus, when i was in my passive form, dead but still able to cast spells. It appears that it makes karthus stay in his passive for longer, and he is able to click to knock up the enemies, moving his already dead body to another area. Lets just say this got me a quadra, and seems a bit unfair :P. Just to clarify, I was already dead when kalista pressed r, I didnt land and then die. Sorry for not having screenshots or video of this, but it works every time and just doesn't seem like it should be possible.