Elastic search strange highlighting behaviour

es_highlight_weirdness.sh

export ES='http://localhost:9200'


# avoid colorizing when using less
if [ -t 1 ]; then
	alias pp='python -mjson.tool | pygmentize -l javascript'
else
	alias pp='python -mjson.tool'
fi

curl -s -XDELETE $ES/highlightdebug > /dev/null
curl -s -XPUT $ES/highlightdebug -d'{
	"index": {
		"number_of_shards": 1,
		"number_of_replicas": 0
	}
}' > /dev/null

curl -s -XPUT $ES/highlightdebug/testdocs/1 -d'{ "title":"cheese" }' > /dev/null

curl -s -XPOST $ES/highlightdebug/_refresh > /dev/null

# uncomment the following to see which commands are executed

echo "\n\ndoes highlight:"
curl -s $ES/highlightdebug/_search -d'{
	"query": {
		"bool": {
			"must": [{
				"constant_score": {
					"query": {
						"term": { "title": "cheese" }
					},
					"boost": 1.0
				}
			}]
		}
	},
	"highlight": {
		"fields": { "title": {} }
	}
}' |pp

echo "\n\ndoesn't highlight:"
curl -s $ES/highlightdebug/_search -d'{
	"query": {
		"bool": {
			"should": [{
				"constant_score": {
					"query": {
						"term": { "title": "cheese" }
					},
					"boost": 1.0
				}
			}]
		}
	},
	"highlight": {
		"fields": { "title": {} }
	}
}' |pp

echo "\n\ndoes highlight"
curl -s $ES/highlightdebug/_search -d'{
	"query": {
		"bool": {
			"should": [{
						"term": { "title": "cheese" }
					}]
		}
	},
	"highlight": {
		"fields": { "title": {} }
	}
}' |pp

results.txt

does highlight:
{
    "_shards": {
        "failed": 0, 
        "successful": 1, 
        "total": 1
    }, 
    "hits": {
        "hits": [
            {
                "_id": "1", 
                "_index": "highlightdebug", 
                "_score": 1.0, 
                "_source": {
                    "title": "cheese"
                }, 
                "_type": "testdocs", 
                "highlight": {
                    "title": [
                        "<em>cheese</em>"
                    ]
                }
            }
        ], 
        "max_score": 1.0, 
        "total": 1
    }, 
    "timed_out": false, 
    "took": 2
}


doesn't highlight:
{
    "_shards": {
        "failed": 0, 
        "successful": 1, 
        "total": 1
    }, 
    "hits": {
        "hits": [
            {
                "_id": "1", 
                "_index": "highlightdebug", 
                "_score": 1.0, 
                "_source": {
                    "title": "cheese"
                }, 
                "_type": "testdocs"
            }
        ], 
        "max_score": 1.0, 
        "total": 1
    }, 
    "timed_out": false, 
    "took": 1
}


does highlight
{
    "_shards": {
        "failed": 0, 
        "successful": 1, 
        "total": 1
    }, 
    "hits": {
        "hits": [
            {
                "_id": "1", 
                "_index": "highlightdebug", 
                "_score": 0.30685282, 
                "_source": {
                    "title": "cheese"
                }, 
                "_type": "testdocs", 
                "highlight": {
                    "title": [
                        "<em>cheese</em>"
                    ]
                }
            }
        ], 
        "max_score": 0.30685282, 
        "total": 1
    }, 
    "timed_out": false, 
    "took": 0
}