Wrong term search result with case_insensitive=true

I have a problem with a specific search when using a term query and case_insensitive=true.

To demonstrate that I've created a shell script.
It deletes then creates index "a" with an attribute "my_kw" of type "keyword".
One document is stored with a value of "Gamma--MÖma" for "my_kw".

Then a term search is executed with value "Gamma--MÖma", it finds the document (as expected).
Then the search is executed with "gamma--mÖma" and case_insensitive=true, it finds the document (as expected).
But then a search is executed with "gamma--möma" and case_insensitive=true. Here it finds nothing, which comes unexpected.

Any idea why it is so?

The script:

# Setup:
CONNECTION="--cacert http_ca.crt -u elastic:xbsv-AdsDWOcefIGzyzJ https://localhost:19200"
set -vx

# Delete old index
deleteIndex() {

# Set up index with mappings
createIndex() {
curl -XPUT $CONNECTION/$INDEX -H 'Content-Type: application/json' -d '{
  "settings": {
    "analysis": {
      "analyzer" : {
        "automatic_analyzer" : {
          "filter" : [
          "tokenizer" : "standard"
    "number_of_replicas": "0",
    "number_of_shards": "1"
  "mappings": {
    "properties": {
      "my_kw": {
        "type": "keyword",
        "store": true

# $1 - doc id
# $2 - keyword value
function insert() {
        ( echo -n '{"my_kw": "'$2'"}' ) | curl -XPOST $CONNECTION/$INDEX/_doc/$1 -H 'Content-Type: application/json' -d "@-"

# $1 - search term
# $2 - case_insensitive false/true
function search() {
echo "===== Search ======"
curl -XPOST $CONNECTION/$INDEX/_search -H 'Content-Type: application/json' -d '
  "query": {
    "term" : {
        "my_kw": {
          "value": "'$1'",
          "case_insensitive": '$2',
          "boost": 1
' | tr , \\012

insert 1 "Gamma--MÖma"
sleep 2

# Searching with correct case and case_insensitive false => expect and get one hit
search "Gamma--MÖma" false 
# Searching with wrong case, but umlaut in correct case  and case_insensitive true => expect and get one hit
search "gamma--mÖma" true 

# Searching with wrong case (umlaut also)  and case_insensitive true => expect one hit, but get no hit
search "gamma--möma" true


Read this post.

Thanks for the hint, but in this case a terms query is not used, but a term query!

The term query supports the case_insensitive flag.

Sorry for the misunderstanding.

In fact, this Ö character doesn't seem to be converted using case_insensitive.

Anyway, using the normalizer as the one in the post above said, you will be able to solve it..

Sorry from me too. I have overread the note on case_insensitive in Term query | Elasticsearch Guide [8.2] | Elastic.
"Allows ASCII case insensitive matching ..."
That was so unexpected to me ...


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