Using Pick Block on the following mobs listed below won't give you the new spawn eggs added in 16w20a, instead the spawn eggs listed below also:

Wither Skeleton - Spawn Skeleton
Stray - Spawn Skeleton
Husk - Spawn Zombie
Elder Guardian - Spawn Guardian
Cat - Spawn Ocelot
Donkey - Spawn Horse
Mule - Spawn Horse
Skeleton Horse - Spawn Horse
Zombie Horse - Spawn Horse

Steps to reproduce:
1. Create a new creative world.
2. Spawn all of the mobs listed above with the new 1.10 spawn eggs or find them spawning naturally.
3. Use the Pick Block Key on them.