Gangplank HUD Ulti Cooldown

I just played GP, and, when I got dove by rumble, I used my ulti as I was dying to try to pick up the kill. We ended up killing each other. It was the first time I used ulti that game, and with no upgrades. When I came back to life, the HUD said my ulti was up, but I tried using it and it wouldn't go off until a few minutes later, which is probably when it would've come up anyway.

I'm sorry I don't have other info rn, but I thought I'd report