[GAMEPLAY] Kennen Ultimate Cooldown Bug?

I played an ARAM game in which I was Kennen and I pressed R right before dying. Once I spawned the ultimate ability was available and wasn't on cooldown, I thought I had it since maybe it didn't go off before I died and ended up running into the enemy team without it. I was confused so I pinged my ultimate and it showed that it was on cooldown in chat, but it appeared as if it was accessible and ready to use in the ability kit. I even took a quick screenshot getting a bit bitter over it (looking at timestamps, the time my ultimate should've been up is at 11:52, but as you can see - the ability doesn't appear to be on cooldown and it was 11:35).

I thought it might've been an unlucky glitch/bug but I attempted to do it again in practice tool by getting executed to towers and use Kennen's ultimate right before getting hit by the last tower shot to kill him - when he spawned, his ultimate showed as if it's ready but when I pinged it in chat, it showed that it was on cooldown.

1. Kennen needs to be very low on health
2. Press R right when you're about to die from an enemy or tower (rather difficult to time it intentionally, pretty easy to pull it off when you panic and try to do something before dying though)
3. Once you respawn, your R ability will not appear to be on cooldown unless you ping it in chat

I know it might be a rather trivial bug since it's hard to pull it off (activating the ultimate right before dying) but when it happens, it might confuse the player and make them jump into a team fight, thinking they have their ultimate up. Will appreciate it if anyone would look into the matter.