Social Zombies not affected by /gamerule doMobSpawning

Confirmed in 13w21b.

This needs to be seen. It poses a serious threat to my adventure map.

Confirmed for 13w23b.

Confirmed for 1.7.2. Why it wasn't fixed for such a long time yet?

Still a concern in 14w08a.

Cannot reproduce as of 15W50A

Reopened, can still reproduce in 15w51b. Adding reproduction steps to description.

Easily observable if you stand in the middle of a ring of fire. The zombies will walk towards you and will keep spawning new ones. (MC-75401)

I can reproduce it in 15w51b :
You should be in a generated world with hard mode(that may help). Eventually kill other mobs to avoid being annoyed by mob spawning cap :

/gamerule doMobSpawning false
/kill @e[type=!Player]
/summon Zombie ~ ~1 ~ {Attributes:[{Name:zombie.spawnReinforcements,Base:1.0d}]}

Use the above command to spawn zombie that will try to spawn another zombie when hit (it still may fail if no correct spawn location are found)

Hit this zombie a few times (~10 times or more if they still don't spawn), and you should see some other zombie coming/spawing.

It is now fixed.

The reason I couldn't reproduce it in the first place is that the reinforcement effect is only effective in Hard and my test world was in Normal.