Search_as_you_type and highlight

Elastic Stack Elasticsearch
2 
PUT test
{
  "mappings": {
    "properties": {
      "my_field": {
        "type": "search_as_you_type"
      }
    }
  }
}

PUT test/_doc/1
{
  "my_field": "quick brown fox jump lazy dog"
}

GET test/_search
{
  "query": {
    "multi_match": {
      "query": "brown fox ",
      "type": "bool_prefix",
      "fields": [
        "my_field",
        "my_field._2gram",
        "my_field._3gram"
      ]
    }
  },
  "highlight": {
    "fields": {
      "my_field": {
        "type" : "unified"
      }
    }
  }
}

That leads to the result:

    "hits" : [
      {
        "_index" : "test",
        "_type" : "_doc",
        "_id" : "1",
        "_score" : 0.8630463,
        "_source" : {
          "my_field" : "quick brown fox jump lazy dog"
        },
        "highlight" : {
          "my_field" : [
            "quick <em>brown</em> <em>fox</em> jump lazy dog"
          ]
        }
      }
    ]

It will only highlight matching tokens — if you leave out the space after fox, it won't mark that. Are you expecting partial highlighting instead? Not sure this would make sense for an autocomplete / search as you type field.