spawn-animals and spawn-npcs=false removes all villagers and prevents summoning new mobs

Setting spawn-npcs=false in server.properties disables villagers completely
Setting spawn-animals=false prevents any mob from being spawned by commands or mob spawners.

What I expected to happen was...
Villagers and animals to stop naturally spawning.
Mobs to still be allowed to be summoned via commands

What actually happened was...
ALL Villagers, including pre-existing ones in the world, or ones newly placed via spawn eggs, disappear instantly.

Steps to Reproduce:

1. Run a server

2. Change server.properties to:

   spawn-npcs=false
   spawn-animals=false
   spawn-monsters=false

3. Join the server and execute the following commands

   /summon villager
   /summon wolf
   /summon zombie

With difficulty on non-peaceful, you can see the Zombie summons fine. But the Villager and Wolf do not stay in the world.

For custom maps, commands should override any server.properties as it does with hostile mobs.