Summoning a horse with NBT data sets its health to 53 and ignores attribute data

Whenever you use /summon for a horse, and provide NBT data in the command, like /summon horse ~ ~ ~ {Tame:1b}, it will spawn with 53 health, and it will ignore any data in the Attributes tag, i.e. {Attributes:[

{Base:0.3375,Name:"generic.movementSpeed"}

,{Base:20,Name:"generic.maxHealth"}]} will still spawn a horse with 53 health and a random movement speed