[GAMEPLAY] Vel'Koz Ult not working

Toward the end of the match my R button wouldn't fire my ult. I changed it to other letters but it still wouldn't fire. While I was dead I would press R and it would tell me that the ability couldn't be used right now(or whatever it says) and after i revived it still would do nothing when pressed. It also wouldn't work by clicking on the ult with my mouse and trying to fire it that way. I tried typing in chat "R" and every time i tried it would send fine, but then I would try to use my ult and it wouldn't fire. I was never silenced or did not have some kind of negitive buff or effect on me. I was using it for most of the game and then at the end it stopped working. The "R" button worked fine in chat like i said, and it registered when I tried changing the hotkey from "R" to "T" and back again. I don't know how to reproduce the bug. I played 8 matched wih Vel'Koz tonight and this only happened durring the matched which is linked above. Thanks, I hope this isn't a bad report :P