[GAMEPLAY] Weird interaction between Unsealed Spellbook and Hexflash

So, I've played a game against a Braum who started with Flash/Exhaust and had Unsealed Spellbook and Hexflash.

During late game, he used Exhaust despite having Hexflash/Ignite on the scoreboard. We could not see that he had exhaust but he had it and used it multiple times, yet the scoreboard always shown Hexflash/Ignite.

I don't know how it works or how to reproduce it tbh, but it's something that you should look at.

Here's the link of the match from the match history: https://matchhistory.euw.leagueoflegends.com/en/#match-details/EUW1/3599160116/211013919?tab=overview