Elasticsearch - Highlight of wildcard

[Nikesh]

Hi,

I have found a behaviour of highlight of wildcard little different.
When I search using single "" i.e., a wildcard character, It does not highlight any of the values.
But if I do the same using two or more "" i.e., wildcard character, It does highlight all the values.
Although the results fetched are the same, why is there such a difference in highlight?
example : 1. Multiple wildcards

{
    "from" : 0, "size" : 10,"_source": {"includes":["ID"]
},  "query": {
    "bool": {"should": [   {
    "bool": {"must": [ {
          "query_string": {
            "query":"**",
            "fields":["ID"]
}}]}}],"minimum_should_match":1}},"highlight": {
        "type" : "unified",
           "fragment_size" : 0,
           "order":"score",
			"number_of_fragments" :4,
        "fields": {
            "*": {
            }           	 
        }
    }
   }

Results :

    {
                    "_index": "index_name",
                    "_type": "_doc",
                    "_id": "AUTO",
                    "_score": 1,
                    "_source": {
                        "ID": "AUTO"
                    },
                    "highlight": {
                        "ID": [
                            "<em>AUTO</em>"
                        ]
                    }
                }

2. Singular Wildcard

{
"from" : 0, "size" : 10,"_source": {"includes":["ID"]
}, "query": {
"bool": {"should": [ {
"bool": {"must": [ {
"query_string": {
"query":"",
"fields":["ID"]
}}]}}],"minimum_should_match":1}},"highlight": {
"type" : "unified",
"fragment_size" : 0,
"order":"score",
"number_of_fragments" :4,
"fields": {
"": {
}
}
}
}

Results :

{  "_index": "index_name",
                "_type": "_doc",
                "_id": "AUTO",
                "_score": 1,
                "_source": {
                    "ID": "AUTO"
                }
            }

[Nikesh]

@elastic Could you please provide any inputs?