Silenced... or not

Basically, I was in a game as Soraka A Twisted Fate used Zhonyas Hourglass to avoid death. I put my Equinox (which silences) underneath him as he was invulnerable. Once he got out of Hourglass, the Equinox was still active underneath him, but he was still able to flash away.

I'm guessing he did it so quickly that the game didn't register he was silenced? Not sure. Either way, there's a bug for you.