Bard - bug [ gameplay]

I was in a game as support. About 30 sec before game end, within enemy base I launch the ultimate . Game wrote : Morgana is spell immune and the ultimate did not took action. Next second started countdown shown in the R area-bottom of screen. True, enemy Morgana was there, I am not aware if her black shield was activated. However, I pay attention to details, no friends or foe where affected by ultimate of Bard. I am not a skilled player , I don't have many games with Bard, I suppose I play with this champion 50..60games. Is the only time I met this behavior. Fps was 46, latency 86 ms, I play on a i5/win 7-64b. I was in the old interface that moment. [ usually i play the new version ] Sincerely, Shield