[{quoted}](name=Spicy Rice,realm=NA,application-id=LqLKtMpN,discussion-id=o970kqUi,comment-id=00040000,timestamp=2018-10-08T19:01:02.739+0000)
The only case I could see for this being a bug is the cc not causing jayce to get the kill.
Things like blitz's hook(and a bunch of other crap I forgot about, I haven't messed with this in years, I think janna's tornado also works this way) will still grant a kill/assist even if they don't break a shield and no other damage/effects are applied.
Zyra's second ult proc(unless it was changed), also won't grant an assist/kill, even though it's damageless cc.
It very much is a bug but it's not yasuo specific, and applies to all shields.
Also I forgot how damage/cc interacts with morgana's shield, but I'm fairly sure it was stupid and incosistent as well.
Anyway, applied cc not giving an assist/kill is definitely inconsistent, and considering the changes made(making more abilities give assists), this is the exception and not the rule. So a bug.