/summon Mob and /summon Monster

For some reason, /summon will autocomplete with Mob and Monster, although those are invalid entity names and will not spawn anything.
Steps to reproduce:
1. Open chat
2. Type /summon Mo and then press tab.
3. Notice that the entity names Mob and Monster appear.
4. Run either /summon Mob or /summon Monster, and notice that they have the same effect as running /summon invalid_entity.