Tags IsBaby and IsVillager can't be changed from true to false with /entitydata

Spawn a Zombie, and execute :
/entitydata @e[type=Zombie,r=5]

{IsBaby:1b,IsVillager:1b}

This do work, but when you try again:
/entitydata @e[type=Zombie,r=5]

{IsBaby:0b,IsVillager:0b}

This don't do anything, but the console output say that the value change.