Kindred's Ult Working As Intended?

Straight from the wiki reads,

Lamb's Respite ACTIVE: Lamb blesses the ground under an allied champion or herself for 3 seconds. While inside the area, all units (including champions, minions and monsters; both allied and enemy) cannot be reduced below 10% of their maximum health. Units in the area who reach the threshold cannot be healed while within for the remaining duration. All units within the zone are healed immediately after the blessing ends.

To my understanding (and I can definitely be wrong here), if Kindred ever falls below 10% while in her ult, she can not leave this 0 - 10% range. So if a Soraka healed her in this state, she would cap at 10% max HP.

But what if she activates her ult AT the said threshold.

I added a video that showcases what I believe to be a bug. Slowing it down, I noticed that 2 Mage minion attacks landed on me upon ult activation, prompting the text "Invulnerable" to appear. From there, I was able to freely auto-attack one of the invulnerable minions to regain all of my HP back.

Again, I don't know if this is intended to happen, but this is a ridiculously strong mechanic if it is.

EDIT: I didn't even realize the invulnerable minion was an issue within itself. If it's invulnerable, how is life-steal still going through when I'm technically doing no damage.