Histogram display badly lines

[dadoonet]

Heya,

I inject 1.000.000 docs in an ES cluster.
Docs look like:

{
   "doc":{
      "id":36478,
      "name":"Malia Maxence",
      "dateOfBirth":"1993-12-03",
      "gender":"female",
      "created":null,
      "meta":{
         "id":null,
         "cars":null,
         "shoes":null,
         "toys":null,
         "fashion":null,
         "music":null,
         "garden":null,
         "electronic":null,
         "hifi":null,
         "food":null
      },
      "address":{
         "id":null,
         "country":"England",
         "zipcode":"86767",
         "city":"Liverpool",
         "countrycode":"GB"
      }
   },
   "meta":{
      "id":"person:36478",
      "rev":"1-000000377ae983e70000000000000000",
      "expiration":0,
      "flags":0
   }
}

Basically, I generate randomly 1.000.000 docs with random birthdates.

When I create an histogram, using Lines instead of Bars, it produces strange results:

Here is the dashboard:

{
  "title": "Introduction",
  "services": {
    "query": {
      "idQueue": [
        1,
        2,
        3,
        4
      ],
      "list": {
        "0": {
          "query": "*",
          "alias": "all",
          "color": "#7EB26D",
          "id": 0,
          "pin": false,
          "type": "lucene"
        }
      },
      "ids": [
        0
      ]
    },
    "filter": {
      "idQueue": [
        0,
        1,
        2
      ],
      "list": {},
      "ids": []
    }
  },
  "rows": [
    {
      "title": "Intro",
      "height": "100px",
      "editable": true,
      "collapse": false,
      "collapsable": true,
      "panels": [
        {
          "error": false,
          "span": 9,
          "editable": true,
          "group": [
            "default"
          ],
          "type": "text",
          "mode": "markdown",
          "content": "From SQL to NoSQL\n================\n\nThis demo illustrates how to make sense of your (BIG) data!\n\nSee also [SQL2NoSQL Github repository](https://github.com/dadoonet/sql2nosql).",
          "style": {},
          "title": "",
          "status": "Stable"
        },
        {
          "error": false,
          "span": 3,
          "editable": true,
          "type": "dashcontrol",
          "save": {
            "gist": false,
            "elasticsearch": true,
            "local": true,
            "default": true
          },
          "load": {
            "gist": true,
            "elasticsearch": true,
            "local": true
          },
          "hide_control": false,
          "elasticsearch_size": 20,
          "temp": true,
          "ttl_enable": true,
          "temp_ttl": "30d"
        }
      ]
    },
    {
      "title": "Query",
      "height": "150px",
      "editable": true,
      "collapse": false,
      "collapsable": true,
      "panels": [
        {
          "error": false,
          "span": 4,
          "editable": true,
          "type": "query",
          "label": "Search",
          "query": "*",
          "pinned": true,
          "history": [
            "*",
            "joe",
            "john"
          ],
          "remember": 10,
          "title": "Query"
        },
        {
          "error": false,
          "span": 4,
          "editable": true,
          "type": "filtering",
          "title": "Filters"
        },
        {
          "span": 4,
          "editable": true,
          "type": "hits",
          "queries": {
            "mode": "all",
            "ids": [
              0
            ]
          },
          "style": {
            "font-size": "10pt"
          },
          "arrangement": "horizontal",
          "chart": "bar",
          "counter_pos": "above",
          "donut": false,
          "tilt": false,
          "labels": true,
          "spyable": true,
          "title": "Hits"
        }
      ]
    },
    {
      "title": "Analytics",
      "height": "300px",
      "editable": true,
      "collapse": false,
      "collapsable": true,
      "panels": [
        {
          "span": 6,
          "editable": true,
          "type": "histogram",
          "mode": "count",
          "time_field": "doc.dateOfBirth",
          "queries": {
            "mode": "all",
            "ids": [
              0
            ]
          },
          "value_field": null,
          "auto_int": true,
          "resolution": 100,
          "interval": "1y",
          "fill": 3,
          "linewidth": 1,
          "timezone": "browser",
          "spyable": true,
          "zoomlinks": true,
          "bars": false,
          "stack": true,
          "points": false,
          "lines": true,
          "legend": true,
          "x-axis": true,
          "y-axis": true,
          "percentage": false,
          "interactive": true,
          "tooltip": {
            "value_type": "cumulative",
            "query_as_alias": false
          },
          "title": "Date of Birth"
        }
      ]
    },
    {
      "title": "Results",
      "height": "450px",
      "editable": true,
      "collapse": false,
      "collapsable": true,
      "panels": []
    }
  ],
  "editable": true,
  "index": {
    "interval": "none",
    "pattern": "[logstash-]YYYY.MM.DD",
    "default": "person"
  },
  "style": "dark",
  "failover": false
}

Note I don't use any time picker but I don't think there is any relation to this.