edge_ngram查询高亮问题

功能:自动补全功能
问题:
搜索 "测试" ,高亮匹配的是"<em>测试数据</em>",期望的是"<em>测试</em>数据"
settings

{

  "my_index": {

    "settings": {

      "index": {

        "number_of_shards": "1",

        "provided_name": "my_index",

        "creation_date": "1531985044696",

        "analysis": {

          "filter": {

            "edge_ngram_filter": {

              "type": "edge_ngram",

              "min_gram": "1",

              "max_gram": "20"

            }

          },

          "analyzer": {

            "autoAnalyzer": {

              "filter": [

                "edge_ngram_filter",

                "lowercase"

              ],

              "type": "custom",

              "tokenizer": "keyword"

            },

            "ik": {

              "tokenizer": "ik_max_word"

            }

          }

        },

        "number_of_replicas": "0",

        "uuid": "WJ22jjdPRX6HIY3DFtgFmA",

        "version": {

          "created": "5050199"

        }

      }

    }

  }

}

 Mapping

{

  "my_index": {

    "mappings": {

      "my_index": {

        "properties": {

          "auto_title": {

            "type": "text",

            "store": true,

            "term_vector": "with_positions_offsets",

            "analyzer": "autoAnalyzer",

            "search_analyzer": "standard"

          },

          "title": {

            "type": "text",

            "copy_to": [

              "auto_title"

            ],

            "analyzer": "ik_max_word"

          }

        }

      }

    }

  }

}

query:

GET /my_index/_search

{

  "query":{

      "term":{

          "auto_title":"测试"

      }

  },

  "highlight":{

			"pre_tags":[

				"<em>"

			],

			"post_tags":[

				"</em>"

			],

			"fields":{

				"auto_title":{

					"type":"fvh"

				}

			}

		},

		"_source":[

		  

		  ]

}

搜索结果:

{

  "took": 0,

  "timed_out": false,

  "_shards": {

    "total": 1,

    "successful": 1,

    "failed": 0

  },

  "hits": {

    "total": 1,

    "max_score": 3.9417796,

    "hits": [

      {

        "_index": "zhuanti",

        "_type": "zhuanti",

        "_id": "953",

        "_score": 3.9417796,

        "_source": {

          "title": "测试数据",

          "special_type": "2",

          "description": "测试顶部专测试顶部专测试顶部专",

          "status": "3",

          "id": "953",

          "create_time": "1520495313"

        },

        "highlight": {

          "auto_title": [

            "<em>测试数据</em>"

          ]

        }

      }

    ]

  }

}

这里我希望高亮的结果是"<em>测试</em>数据",不知哪里出了问题