Has_child filter does't work as expected with bool filter?

Elastic Stack Elasticsearch
1

I have a query to return all distinct parent ids that have children with open_flag=1 excluding parent ids that have children with open_flag=0 (open_flag is either 1 or 0 for all chidren). It returns much more results than expected. The list of aggregated contact_ids does include ids where open_flag=0.

The query is performed on alias that have 3 indexes. Elasticsearch version is 1.4.5

{
    "query": {
        "filtered": {
            "filter": {
                "bool": {
                    "must": [
                        {
                            "has_child": {
                                "type": "event",
                                "filter": {
                                    "bool": {
                                        "must": [
                                            {
                                                "term": {
                                                    "open_flag": 1
                                                }
                                            },
                                        ]
                                    }
                                }
                            }
                        }
                    ],
                    "must_not": [
                       {
                           "has_child": {
                                "type": "event",
                                "filter": {
                                    "bool": {
                                        "must": [
                                            {
                                                "term": {
                                                    "open_flag": 0
                                                }
                                            }
                                            
                                        ],
                                        "must_not": []
                                    }
                                }
                            }
                       }
                    ]
                }
            }
        }
    },
    "fields": [],
    "size": 0,
    "aggs": {
        "contact_ids": {
            "terms": {
                "field": "contact_id",
                "size": 1000
            }
        },
        "total_count": {
            "cardinality": {
                "field": "contact_id",
                "precision_threshold": 40000
            }
        }
    }
}