Fiora riposte ineffective on Xin Zhao CC (knock-up)

Quite simple really, if Fiora attempts to use Riposte on Xin Zhao's third strike (knock-up) he does not become stunned. Perhaps Riposte only works against Xin Zhao's CC if she uses it before he goes in with his skill, but alas, it seems to me that Riposte should work when used before his knock-up (on his knock-up) regardless. Just an observation from a previous match.