Bar in a bar chart gets incorrect sorted order when adding a sub-bucket aggregation

[TomonoriSoejima]

Kibana version:
6.2.2
Elasticsearch version:
6.2.2
Server OS version:
Mac OS
Browser version:
Version 66.0.3359.117 (Official Build) (64-bit)

Browser OS version:
Chrome 66 on Mac OS X 10

Original install method (e.g. download page, yum, from source, etc.):
Download page
Description of the problem including expected versus actual behavior:

Steps to reproduce:

I created some data set that lists countries sorted in alphebetical order and within each bar there are 12 elemtents inside execpet the first bar Australia.

This is important to report the odd behavior.
Now what happens is nested aggregation on busy_month.keyword field is not respected.
What happens is the bar's fundation is devired from the botom elemenet found in the very first bar, which in htis case is JUNE.

This problem can be similar to #17532

Request

{
  "size": 0,
  "_source": {
    "excludes": []
  },
  "aggs": {
    "2": {
      "terms": {
        "field": "country.keyword",
        "size": 5,
        "order": {
          "_count": "asc"
        }
      },
      "aggs": {
        "3": {
          "terms": {
            "field": "busy_month.keyword",
            "size": 12,
            "order": {
              "_count": "desc"
            }
          }
        }
      }
    }
  },
  "stored_fields": [
    "*"
  ],
  "script_fields": {},
  "docvalue_fields": [
    "created"
  ],
  "query": {
    "bool": {
      "must": [
        {
          "match_all": {}
        },
        {
          "range": {
            "created": {
              "gte": 1522508400000,
              "lte": 1525100399999,
              "format": "epoch_millis"
            }
          }
        }
      ],
      "filter": [],
      "should": [],
      "must_not": []
    }
  }
}

Response

{
  "took": 8,
  "timed_out": false,
  "_shards": {
    "total": 5,
    "successful": 5,
    "skipped": 0,
    "failed": 0
  },
  "hits": {
    "total": 5000,
    "max_score": 0,
    "hits": []
  },
  "aggregations": {
    "2": {
      "doc_count_error_upper_bound": -1,
      "sum_other_doc_count": 4451,
      "buckets": [
        {
          "3": {
            "doc_count_error_upper_bound": 0,
            "sum_other_doc_count": 0,
            "buckets": [
              {
                "key": "JUNE",
                "doc_count": 79
              }
            ]
          },
          "key": "Australia",
          "doc_count": 79
        },
        {
          "3": {
            "doc_count_error_upper_bound": 0,
            "sum_other_doc_count": 0,
            "buckets": [
              {
                "key": "FEBRUARY",
                "doc_count": 12
              },
              {
                "key": "MARCH",
                "doc_count": 11
              },
              {
                "key": "JUNE",
                "doc_count": 10
              },
              {
                "key": "DECEMBER",
                "doc_count": 8
              },
              {
                "key": "JANUARY",
                "doc_count": 8
              },
              {
                "key": "JULY",
                "doc_count": 8
              },
              {
                "key": "NOVEMBER",
                "doc_count": 8
              },
              {
                "key": "AUGUST",
                "doc_count": 6
              },
              {
                "key": "OCTOBER",
                "doc_count": 6
              },
              {
                "key": "APRIL",
                "doc_count": 5
              },
              {
                "key": "SEPTEMBER",
                "doc_count": 4
              },
              {
                "key": "MAY",
                "doc_count": 2
              }
            ]
          },
          "key": "US",
          "doc_count": 88
        },
        {
          "3": {
            "doc_count_error_upper_bound": 0,
            "sum_other_doc_count": 0,
            "buckets": [
              {
                "key": "APRIL",
                "doc_count": 14
              },
              {
                "key": "JULY",
                "doc_count": 13
              },
              {
                "key": "DECEMBER",
                "doc_count": 11
              },
              {
                "key": "JUNE",
                "doc_count": 11
              },
              {
                "key": "MAY",
                "doc_count": 11
              },
              {
                "key": "NOVEMBER",
                "doc_count": 10
              },
              {
                "key": "OCTOBER",
                "doc_count": 10
              },
              {
                "key": "MARCH",
                "doc_count": 9
              },
              {
                "key": "SEPTEMBER",
                "doc_count": 9
              },
              {
                "key": "FEBRUARY",
                "doc_count": 8
              },
              {
                "key": "JANUARY",
                "doc_count": 8
              },
              {
                "key": "AUGUST",
                "doc_count": 6
              }
            ]
          },
          "key": "KOREA",
          "doc_count": 120
        },
        {
          "3": {
            "doc_count_error_upper_bound": 0,
            "sum_other_doc_count": 0,
            "buckets": [
              {
                "key": "APRIL",
                "doc_count": 14
              },
              {
                "key": "AUGUST",
                "doc_count": 14
              },
              {
                "key": "JULY",
                "doc_count": 14
              },
              {
                "key": "SEPTEMBER",
                "doc_count": 14
              },
              {
                "key": "OCTOBER",
                "doc_count": 13
              },
              {
                "key": "MAY",
                "doc_count": 12
              },
              {
                "key": "JANUARY",
                "doc_count": 11
              },
              {
                "key": "MARCH",
                "doc_count": 9
              },
              {
                "key": "NOVEMBER",
                "doc_count": 8
              },
              {
                "key": "DECEMBER",
                "doc_count": 7
              },
              {
                "key": "FEBRUARY",
                "doc_count": 7
              },
              {
                "key": "JUNE",
                "doc_count": 5
              }
            ]
          },
          "key": "Vietnam",
          "doc_count": 128
        },
        {
          "3": {
            "doc_count_error_upper_bound": 0,
            "sum_other_doc_count": 0,
            "buckets": [
              {
                "key": "JULY",
                "doc_count": 18
              },
              {
                "key": "DECEMBER",
                "doc_count": 16
              },
              {
                "key": "JANUARY",
                "doc_count": 16
              },
              {
                "key": "MARCH",
                "doc_count": 15
              },
              {
                "key": "APRIL",
                "doc_count": 14
              },
              {
                "key": "MAY",
                "doc_count": 10
              },
              {
                "key": "NOVEMBER",
                "doc_count": 9
              },
              {
                "key": "OCTOBER",
                "doc_count": 9
              },
              {
                "key": "SEPTEMBER",
                "doc_count": 9
              },
              {
                "key": "FEBRUARY",
                "doc_count": 8
              },
              {
                "key": "AUGUST",
                "doc_count": 5
              },
              {
                "key": "JUNE",
                "doc_count": 5
              }
            ]
          },
          "key": "UK",
          "doc_count": 134
        }
      ]
    }
  },
  "status": 200
}

[timroes]

Closing this as a duplicate of #17532