[GAMEPLAY] Healing prevents lethal damage

I just had a poro king game where this happened twice. Once when pantheon was about to die to a varus q, the second time when I was about to die to zed ult. The king's heal activated at just the right moment to "revive" us. The health goes blank before repopulating with a small amount. I'm not sure if it correlates to the heal amount.

I also saw a reddit post where a soraka avoided dying to karthus by healing her ally. It looks like this is the same bug.