Elasticsearch field 'copy_to' disagrees with itself

gistfile1.sh

curl -XPUT 'http://localhost:9200/index1' -d '
{
  "mappings": {
    "parent": {
      "properties": {
        "children": {
          "type": "nested",
          "properties": {
            "colour": {
              "type": "string"
            },
            "make": {
              "type": "string",
              "copy_to": "copied"
            }
          }
        }
      }
    }
  }
}
'

curl -XPUT 'http://localhost:9200/index1/parent/1' -d '
{
  "children": [
    {
      "colour": "blue",
      "make": "ford"
    },
    {
      "colour": "red",
      "make": "rover"
    }
  ]
}
'

curl -XGET 'http://localhost:9200/index1/_mapping?pretty=true'
# returns this (note the location of the 'copied' field):
{
  "index1" : {
    "mappings" : {
      "parent" : {
        "properties" : {
          "children" : {
            "type" : "nested",
            "properties" : {
              "colour" : {
                "type" : "string"
              },
              "make" : {
                "type" : "string",
                "copy_to" : [ "copied" ]
              }
            }
          },
          "copied" : {
            "type" : "string"
          }
        }
      }
    }
  }
}

# From looking at the mapping, we would expect this query to return the document (it doesn't):
curl -XPOST 'http://localhost:9200/index1/_search' -d '
{
  "query": {
    "bool": {
      "must": [
        {
          "match" : {
            "copied" : "rover"
          }
        },
        {
          "nested": {
            "path": "children",
            "score_mode": "avg",
            "query": {
              "match": {
                "colour": "red"
              }
            }
          }
        }
      ]
    }
  }
}
'

# From looking at the mapping, we would not expect this query to return the document (it does):
curl -XPOST 'http://localhost:9200/index1/_search' -d '
{
  "query": {
    "nested": {
      "path": "children",
      "score_mode": "avg",
      "query": {
        "bool": {
          "must": [
            {
              "match": {
                "copied": "rover"
              }
            },
            {
              "match": {
                "colour": "red"
              }
            }
          ]
        }
      }
    }
  }
}
'