Both undead horse-types: Skeleton horse and Zombie horse are losing health rather than slowly regenerating health, eventually they die. (Even if they are named and/or not doing anything or being ridden or being near danger.)

This happens in survival-mode and can also be replicated in creative-mode.

(It was in creative mode i also noticed it happened to the unused zombie variant of horses.)

-Both undead horse types still takes damage from splash potions of healing; as they get health from splash potion of harming (since they are undead), so no error there.

Also one odd thing i also noticed:

Sometime when riding a skeleton horse; the lost healthbars were invisible.

See attachment "MC_Win10_Skelhorse take dmg_C 1HP.jpg" for this.

When did it first happen?

After the latest update 1.6.0, when the phantoms were introduced.

(2018-08-29) I had just loaded up my local coop world i use to play with some friends, and started hearing skeletal horse death-sounds (i had about 8 in the main base, 2-4 at another base) and noticed that they were rapidly losing health and dying.

Since they don´t seem to be flashing red (taking damage-red, unless when dead) or giving injured sounds, it was only when they started dying i noticed something was wrong.

Luckily i had just exported a backup, so as soon as this gets fixed i can continue from there..

Possible causes?

My best guess is that somehow the health regeneration is either at an negative value; or it is counted as "healing" which in the game damages undead mobs.

Attached file description:

I always record gameplay with Nvidia Shadowplay, these screenshots (total of 7) are taken when i viewed 3 different clips on VLC. You can see the elapsed time of each of them for perspective on how fast-ish the health depleted for the undead horses.

Thanks for reading, and please fix this.