LeBlanc's ultimate (R) BUG [GAMEPLAY]

So, there's a bug with LeBlanc's ultimate where it won't do any damage. Recently I've experienced it more and more when I use W then R to clear the minion wave and only the first distortion (W) doing the damage. I think I've also experienced once to not do any damage when I use Q then R. That's pretty much about it. To reproduce it just W then R as fast as possible (or not) and sometimes the ultimate (R) won't do any damage.