I haven't played in over a year, and just started up again about a month ago, so a lot has changed. Last time i played, improved exhaust made the target blind... I recently started playing Master Yi more faithfully, and i am noticing a few bugs as time goes on.
The Q, i believe it is supposed to make Yi "untargetable". There has been many instances with against melee and ap heroes where i would cast. Go in the motion, and i would be dead before the motion is even anywhere complete. For example if i would be attacking a hero, i activate Q (no debuffs on me) my cool down would go, no damage would be given to the targeted hero and i would be dead. Granted i am low on HP, but if i go in the motion, the sound goes, the cooldown is now counting, and no damage is done. That's the bug i see with the Q. Basically, if the cool down goes, i am "untargetable", i do the motion, i should ONLY die when i come back from the Q's motion, and the damage SHOULD still happen to the targeted hero.
EDIT: I would like to add that when Q'ing in jungle/laning resets the creeps for a split second and causes them to regenerate HP. Only when only target available is Yi himself. This makes doing dragon solo, and or golem/lizard buffs just a tad bit more difficult.
Now to the R, everything seems to work fine when alive but not on death. For example, Myself, and a team member are attacking 1 hero. I use my R, but die before getting the kill, but the targeted enemy dies with in say 1-2 seconds after i die (a close call sorta deal). Even knowing i get the assist on the kill, it will not reduce the cool down time by 50% as it should. Simple as that for this one, on assist it should reduce cool down and it does not.
EDIT: I just died while in my Q, this time the damage went through... Landed me the kill, but since i died before he did (however the damage order was done). It did NOT reset my cool down counter. Even knowing i got the kill. I the kill was well with in the 8 seconds of his ULT activation also.
I can produce video evidence if needed, i have to buy FRAPS if so. No friends play this game, so it will be hard to reproduce the R cool down one on my own. Assuming RIOT has a team for this though, and can spare me the money. I think that's about it though for now. I will edit if anything else happens to be found.
I am supposed to provide steps to produce the same situation i am experiencing. I briefly described above.
Q - Untargetable: 1 Enemy Champion, Yourself as Master Yi, Fighting until low hp on Yi, and say 200-300 hp remaining you would Q at the target enemy hero (as that are attacking), your cool down activates, you go through the motion & sound, no damage is done to enemy hero and you die before coming out of it.
Q - Yourself as Master Yi, Q into the Lizard Buff (dragon, golem etc) you kill both minions (or not doesnt matter), you auto attack, and then Q again. This would briefly reset the Lizard until you come back out of Q but the Lizard has now gained some HP. From the testing i did, i couldnt keep the lizard/golem still while avoiding hitting them. So i pulled them away slightly and then Q'd once off cooldown. It did reset their hp a small portion.
R - 1 Enemy Champion, Yourself as Master Yi and a Team member say Garin, Fighting until low hp on Yi, and say 200-300 hp remaining, and 200-300hp remaining on the enemy hero. You are all fighting, Master Yi activated R and dies, then Garin uses ultimate and insta kills the enemy 2 seconds after you died. You get the assist, but not the 50% time off Master Yi's R.