Summoning slimes with custom maxHealth attributes does not work

Description:
Summoning slimes (Normal & Lava) with custom maxHealth attributes don't works:

summon magma_cube ~ ~1 ~ {Health:1000.0f,Attributes:[{Name:"generic.maxHealth",Base:1000.0d}]}

But this (with Zombie) works:

summon zombie ~ ~1 ~ {Health:1000.0f,Attributes:[{Name:"generic.maxHealth",Base:1000.0d}]}

Actual: Summoned slimes use default value of maxHealth instead of the one given.
Expected: Should use maxHealth from summon command instead of default.

Code analysis by Marcono1234 can be found in this comment.