Malzahar Mana Bug

I was in a custom game to test my new snow day malzahar skin. The mana cost on his w said 60 mana when it was rank 3. I had more than 60 mana and it wouldn't go off (it was not on cooldown). It did go off earlier when I was full mana. According to the lol wiki it should cost 80 mana, but that was not what was being displayed. Thanks, jonjonjon63.