Yasuo Ultimate Mechanical Inconsistency [RIOT CONFIRMED]
Yasuo's ultimate has five conditions. The first, his ultimate must be in range (obviously), its not global. Second, the target must be "airborne". This means any displacement in the game from Vayne's condemn to Draven's stand aside is fair game to ult off of. Thirdly, Yasuo must have vision on the target, invisible targets, even if airborne, cannot be hit. Fourthly, (when ulting multiple people) champions must be within a certain range of each other. The fifth and final condition is a much lesser known mechanic. Yasuo must be facing the target he is attempting to ult. If Yasuo is running away from the target, the ultimate will not go off. It has come to my attention that not a lot of people are aware of this mechanic. Some are even going as far as to claim that this is a bug.
Yasuo ultimate "bug" (but it's not actually a bug): https://youtu.be/bASBJIL6LVQ?t=1m32s
I spent over an hour live chatting with Riot and 6 Yasuo main's amongst them concluded that this IS in fact how Yasuo's ultimate is supposed to work. However, they also said it was inconsistent. Some people could replicate it easily, some had more trouble. I was personally asked to make this post so that Riot would be aware of this and "Keep an eye on it".