Issue with embedded document uniqueness

HI there,

I am upgrading mongoengine from 0.8.6 to 0.10.6 and I am hitting issue when saving one of my models.

DuplicateKeyError: E11000 duplicate key error index: mbc_web.level_one.$list_level_twos.en_name_1 dup key: { : "Ambulance/Medical Travel" } 

As you can see from my models, I have define 3 unique fields on the LevelTwo model (l2_id, en_name, fr_name fields) as I would like LevelTwo model to be unique within the LevelOne.list_level_twos array. but not unique in the whole document. I would like to be able to have 2 LevelOne models that could have list_level_twos array that contains the same LevelTwo model

This used to work with 0.8.6, is there a option I need to include get the same functionality has before

Models:

class LevelTwo(db.EmbeddedDocument):
    l2_id = db.ObjectIdField(required=True, unique=True)
    en_name = db.StringField(max_length=80, required=True, unique=True)
    fr_name = db.StringField(max_length=80, required=True, unique=True)
    list_level_threes = db.ListField(db.EmbeddedDocumentField(LevelThree), default=[])

    def __repr__(self):
        return '<Provider: %r>' % self.en_name


class LevelOne(db.Document):
    en_name = db.StringField(max_length=80, required=True, unique=True)
    acronym = db.StringField(max_length=10, required=True, unique=True)
    fr_name = db.StringField(max_length=80, required=True, unique=True)
    government = db.BooleanField(required=True)
    display_order = db.IntField(min_value=0, max_value=100000, unique=True, required=True)
    list_level_twos = db.ListField(db.EmbeddedDocumentField(LevelTwo), default=[])

    def __repr__(self):
        return '<Client: %r>' % self.en_name

Start by reproducing the DuplicateKeyError with the LevelOne and embedded LevelTwo models shown in the issue, then inspect how the embedded unique fields are indexed. Compare the behavior between mongoengine 0.8.6 and 0.10.6 and determine whether the requested per-parent uniqueness is supported; done means the expected behavior or required option is documented and covered by a regression test.