Zombie Horses & Skeleton Horses gradually lose health & die from nothing

After spawning in a Zombie Horse and a Skeleton Horse, both seem to die randomly after some time has passed. Neither of them were damaged by any means.

Edit by Zeb: After some testing, it looks like the skeleton/zombie horses slowly lose health over time for no apparent reason, before finally dying. They make NO death sound when they die and drop no items. The cause of this bug is that horses gradually regenerate health over time, through the "healing" effect. But since zombie horses & skeleton horses are undead mobs, this healing effect actually damages them.