Fiora VS Udyr

Not sure if this is a glitch in programming or how it's meant to work but here's the issue I've been finding. Riposte stops gangplank Q, nasus Q, and basically all spell based empowered auto attacks. So why is it riposte is worthless against Udyr tiger and bear stance. You riposte the bear stance proc, well cool Udyr takes some damage but you still are stunned and take stun damage, so riposte goes off but doesn't stop any of his damage or the stun. Then you go to Tiger stance and same thing, you "riposte" his tiger proc but oh wait his initial attack still does damage and you still take the bleed damage. So am I missing something here or is Udyr's skills written in such a different manner then any other empowered AA champion?