Bug with Karthus's Q's if Passive is Procced

https://plays.tv/s/LEJmS2ljtYNF

In this video you can see that while Karthus was casting Q's, he got put into passive, however the Q that he managed to cast just before hand seemed to fizzle out and disappear after going into passive. This ended up turning what could've been a double into nothing at all.

Now I don't know whether or not Riot is going to fix this with their talk of Spell Buffering regarding Karthus and Ryze, but if it doesn't fix this issue, I'd like to bring this up. Also, something similar happens a lot of the time if you manage to cast a Q just before the passive ends, where the Q will just sort of fizzle out.

(Note: The video wasn't of me, it was made by the main mod of Reddit's r/Karthusmains boards. Just thought I'd mention :P )