Untargetable Yi's Alpha Strike VS Fizz's Playful/Trickster

I'm playin Master from time to time and i have noticed something which i think is not right; when you alpha strike you become untargetable but receive damage from aoe (alright) or get stunned or snared, here is the LoL description of Yi's Alpha Strike:

• Master Yi teleports across the battlefield with blinding speed, dealing physical damage to multiple units in his path, while simultaneously becoming UNTARGETABLE. Alpha Strike can critically strike and deals bonus physical damage to minions and monsters. Basic attacks reduce Alpha Strike's cooldown. If you only look at it like this every thing is right but when you look at Fizz's Playful/Trickster (i still took these info from LoL) :
• Fizz hops into the air, landing gracefully upon his spear and becoming UNTARGETABLE. From this position, Fizz can either slam the ground or choose to jump again before smashing back down. The same Untargetable effect apply, but when in the untargetable stat fizz wont get stunned, snared, etc or receive damage at all, so i was wondering why. Those abilities are clearly working the same way but it seems like the one from fizz is simply not writen rightfully or the thing is broken. Tkx in advance for your comments