Zed Ult Bug

When playing Zed, I ult on to someone but if they attack where I was before i ulted they would kill me during the untargetable frames such as when a kallista uses her q ability where i originally was while i ult her it kills me and my ult goes on cooldown. Is this a bug or has this always been this way because I've noticed it recently same thing happens with Riven w and ravenous hydra.