HP tamed dog

Hello,

I have a problem, i want to increase the health point of my tamed dog, with this command :

/entitydata @e[type=Wolf] {Attributes:[

{Name:"generic.maxHealth",Base:500}

],Health:500.0f}

For a NORMAL dog, it works, but for a tamed dog, it not works and there is a strange effect when i hit him (screenshot).

I have try if it's not me who hit him, with an another player, but it's the same, he dies very quickly.

It is a bug or i made a mistake with something ?