Immortal Yorick Ghoul

I was just playing an ARAM with a Yorick on my team. At some point, one of his ghouls became immortal:

Here it is attacking the turret: http://i.imgur.com/UA8ZKAs.jpg

Same ghoul, 10 seconds later. Note that Yorick is dead: http://i.imgur.com/cHNMBoQ.jpg

Same deal (now in front of the turret) over a minute later: http://i.imgur.com/o1kn6Wf.jpg

Just hanging out: http://i.imgur.com/e7IO2Vt.jpg

Nothing the enemy team did to this guy could kill it. It lasted until they surrendered.