Ahri charm/Malphite ult interaction

Very weird interaction, have not had time to reproduce, but I was charmed as I was spamming R to ult, my ult went on cooldown, but there was no sound played, no movement made, and no damage displayed, it was as if it just was burned. I saw someone do it in a video too, so it clearly is a already known issue, just thought might be important to see.