[mongoose] Schema validation

I am experimenting with specifying nested objects in schema in the following two forms:

1st form:

var UserSchema = Schema({
  name: {
    first: {
      type: String,
      required: true
    },
    last: {
      type: String,
      required: true
    }
  }
});

2nd form: (Note that "default" is also honored.)

var UserSchema = Schema({
  name: {
    type: {
      first: {
        type: String,
        required: true
      },
      last: {
        type: String,
        required: true
      }
    },
    default: {
      first: 'Foo',
      last: 'Bar'
    }
  }
});

However, with the 2nd form, the "required" validation is being ignored by Mongoose. I understand that "object" is not one of the 7 schema types, but since things other than validation seems to work, I'd expect validation to work as well.

Is this by design?