[GAMEPLAY] Fiora ultimate is cancelled and set into cool down when used on an enemy Fiora

Recently was playing a game as Fiora and was laning with an enemy Fiora. Whenever we dueled, she would use her ultimate on me, which worked for her. But when I used it on her, no ultimate showed up around her, no vitals were able to be struck around her, and to make it worse, my ultimate was set into cool down, without it being used once! This happened more than once in the single game. To reproduce it simply lane with another enemy Fiora (I do not know if this occurs with other champions, but it only happened against an enemy Fiora, I suspect it happens when we both use it at the same time), and try using your ultimate on her. Instead of having all four vitals show up, nothing happens, and your ultimate is set into cool down.