Morde W passive not present/visual?

So I just got Morde in an ARAM game. I noticed I didn't get that fancy thing I got when killing minions that indicated Morde's W passive was in effect. I noticed the description of the W was lacking it, too. Is this a bug or simply an undocumented change? It hardly affects him in Summoner's Rift, I assume, because nobody takes him botlane anymore, but still.