Kibana doesn't understand date_nanos datatype

[rnd-ash]

Kibana version:
7.0.0RC1
Elasticsearch version:
7.0.0RC1
Server OS version:
Ubuntu 16.04 AWS
Browser version:
Chrome

Describe the bug:
I recently updated the mappings in my cluster to allow for microsecond storage using the following query to elasticsearch:

PUT /_template/event-template?include_type_name=true
{
  "template": "event-*",
  "mappings": {
    "_doc": {
      "properties": {
        "Event-Timestamp-UTC": {
          "type": "date_nanos"
        }
      }
    }
  }
}

The Event-Timestamp-UTC field used to be a standard Date field prior to my re-mapping.
After re-mapping and deleting all the old data from elasticsearch, Kibana shows the following for the field:

[timroes]

Duplicate of #31424