elasticsearch weird behavior when a document's _id is set to an object

gistfile1.sh

# When indexing a document, we can specify an _id in the source to get ES to store it
curl -XDELETE 'http://localhost:9200/testindex/'
curl -XPOST 'http://localhost:9200/testindex/people/50f626ce173183f5f2d9dec0?refresh=true' -d '{
    "_id" : "50f626ce173183f5f2d9dec0",
    "person" : {
        "age" : 25,
        "name" : "Bob"
    }
}'
# And we can now find this document with say, a range query:
curl -XGET 'http://localhost:9200/testindex/_search?size=1' -d '
{
    "query": {
        "filtered": {
            "filter": {
                "range": {
                    "person.age": {
                        "from": 20,
                        "to" : 30
                    }
                }
            }, 
            "query" : {
                "match_all" : {  }
            }
        }
    }
}'

# If we specify an _id that doesn't match the id in the url, ES (correctly) throws an error
curl -XDELETE 'http://localhost:9200/testindex/'
curl -XPOST 'http://localhost:9200/testindex/people/50f626ce173183f5f2d9dec0?refresh=true' -d '{
    "_id" : "some_other_id",
    "person" : {
        "age" : 25,
        "name" : "Bob"
    }
}'
# Returns:
# {"error":"MapperParsingException[Failed to parse [_id]]; nested: MapperParsingException[Provided id [50f626ce173183f5f2d9dec0] does not match the content one [some_other_id]]; ","status":400}


# However, if we set the document's _id to an object, ES doesn't complain
curl -XDELETE 'http://localhost:9200/testindex/'
curl -XPOST 'http://localhost:9200/testindex/people/50f626ce173183f5f2d9dec0?refresh=true' -d '{
    "_id" : {
        "$oid" : "50f626ce173183f5f2d9dec0"
    },
    "person" : {
        "age" : 25,
        "name" : "Bob"
    }
}'


# In this case where the _id is set to an object, we can no longer find the object with a range query.
curl -XGET 'http://localhost:9200/testindex/_search?size=1' -d '
{
    "query": {
        "filtered": {
            "filter": {
                "range": {
                    "person.age": {
                        "from": 20,
                        "to" : 30
                    }
                }
            }, 
            "query" : {
                "match_all" : {  }
            }
        }
    }
}'
# Returns:
# {"took":1,"timed_out":false,"_shards":{"total":5,"successful":5,"failed":0},"hits":{"total":0,"max_score":null,"hits":[]}}

# But, if we take out the range, we can still see that the object exists
curl -XGET 'http://localhost:9200/testindex/_search?size=1' -d '
{
    "query" : {
        "match_all" : { }
    }
}'

# It looks like when the _id is set to an object, the document isn't getting correctly indexed.  
# I think ES should probably be throwing an error when trying to index a document with a non-string _id.