Not sure if this is intended or not, but I was doing some solo Inferno earlier today, and had just rescued the Templar from the Ritual and was headed down to kill Jondor. Immediately after we got his equipment and headed towards Jondor, we hit a Rare Vampiric Desecrator. As I was attacking it, I noticed that its health didn't go down at all. After a little time at it, I thought it might be because my follower wasn't leaving the Desecration spots, and was feeding the rare.

So, I dismissed my follower to take the Rare on myself, and continued to engage, noticing that his HP Bar still wouldn't move. After a little more time, I realized the root cause was because the character I had rescued -- The Templar, who I couldn't dismiss, was meleeing the Rare, and with an infinite pool of HP, couldn't be killed. The Rare was continuously desecrating the Templar, and was topping off his HP repeatedly, and no amount of damage I could do to the Rare was making a dent in his health.

Hopefully not intended, but thought I would report.