Yasuo's shield executes if no extra damage is done

Just had a game where an enemy Yasuo tanked tower and I alpha strike with Yi then run around to hopefully get away, and it eats the shield and he executes. Its a shield and being a support main I was pretty sure Janna's shield worked the opposite and tested it (gets killed not executed) This is a bug as Morgana shielding all damage also gets killed instead of executed. Either shields aren't being registered properly or Yasuo's shield has a special defining characteristic which I don't understand or Yasuo's shield is glitched.

twitch.tv/jamorelol/v/52069196 -Yasuo execute twitch.tv/jamorelol/v/52069290 -Janna killed in test

Also the way links to twitch work doesn't appear to work well either as the link with the post goes straight to my stream instead of the highlight. Weird.