Azir Ult Cooldown Timer

Hi, I was playing azir a few games ago, and I used my ultimate right before dying. The ultimate went out as normal, knocking everyone back, and I died. Sounds normal, right? However, when I respawned, I noticed that my ultimate was (or appeared to be) off cool down, as if it never set. I smiled to myself, and trotted happily into a 1v2, knowing I would have my ulti should I need to escape. However, lo and behold! Upon pressing R, nothing happened, and the ability was still on cool down, despite it's appearing in the toolbar as available.

This was later confirmed a couple games later as I played against an azir, who "thought his ulti was up, but it wouldn't go off."