Spawner's entity display defaults the values of NBT data to basic value, rather than mobs' default

Spawner's entity display defaults the values of NBT data to basic value, rather than mobs' default.

Here are some examples:

1. Goat in the monster spawner has no horns.
2. Skeletons, strays and wither skeletons in the monster spawner has no weapon.

This is basically the same as spawn mob using "/summon <mob>", and the spawner display using "/summon <mob> <x> <y> <z> {}"; this is probably because the spawn data is required to have the id set.