Horse Bug - Horse Dies When LAN Connected Player Dismounts

Please repair this bug. It happens when I host a world on LAN and my friend joins. We spawn horses in with creative mode then go to survival. F =host R = player that joined world. For F there are no glitches but for R whenever he gets off a horse he has a random chance to kill it. Horses randomly die for R when he gets off of them. R is not holding a sword or bow in hand neither any weapon. Nothing is shooting the horse. It just dies randomly when R gets off. Sometimes it won't die but sometimes it will. I hope you understood me and please fix this also there are many bugs for R players. Thanks already . I have no attachements sorry but it happens quite often.

Addition by [Mojang] Mega_Spud (Jay Wells)
Temporary Workaround
If the player dismounts the horse when in shallow water, the horse shouldn't take damage.