using entitydata @e {id:"zombie"} doesn't update the entity

If I use the EntityData command at any entity to change the type of the entity, the entity doesn't visually change.

Steps to reproduce:

/summon Sheep
/entitydata @e[type=Sheep] {id:"Zombie"}

More in-depth:

The entity class doesn't change with the entity data.

Possible fix:

Re-build the entity (use the readNBT function) using the changed NBT to correct the entity type.