Vel'Koz Ultimate whiffs

I'm not entirely sure how i did it... but there is a bug with Vel'Koz where if you attempt to cast E and then R immediately afterwards, neither spell affects the field, but the Ultimate will play the animation on Vel'koz while the channel indicator bar appears on the screen, giving the illusion that Vel is just staring at his target really hard. After that, the ability goes on cool-down with no attempted damage done.

I did this last night in an ARAM game, my mouse was clearly not malfunctioning, as I attempted to do it again after re-spawning and it worked fine. I tried to recreate the same situation, but was unable to (game didn't last much after that).

Has anyone else had this issue?