Targeted ability interaction with Fizz's Playful/Trickster

Was playing Nasus top. Fizz roamed up to dive me, moment he goes in tower range I use wither, it goes on cooldown and mana was used, just as I cast it, Fizz used Playful/Trickster and I noticed that wither never went on him. Not sure if Playful/Trickster is meant to remove something like wither or cause it to have full cooldown and mana cost, but I believe this is a bug.

I don't have a video (my internet isn't good enough to stream, and I get too much of an FPS spike to record)