It looks like there can be some implicit conflicts around index_name and multi-fields. This is likely an edge case, but could cause some very funky behavior.

gistfile1.txt

curl -XDELETE 'http://localhost:9200/test/'

curl -XPOST localhost:9200/test/ -d '{
  "mappings" : {
  "test":{
      "properties" : {
        "multi_test" : {"type":"string", "index_name":"multi_test.string"}
      }
    }}
  }
}'

curl -XPOST localhost:9200/test/test/_mapping -d '{
"test":{
    "properties" : {
      "multi_test" : {
         "type":"multi_field", 
         "fields": {
            "string" : {"type" : "string", "index_name":"multi_test.string"},
            "multi_test" : {"type":"float", "index_name":"multi_test.float"}
         }
      }
    }
  }
}'


curl -XPUT localhost:9200/test/test/1 -d'{
  "multi_test": "10000"
}'

curl -XPOST 'http://localhost:9200/test/_refresh'

curl 'http://localhost:9200/test/test/_search?q=multi_test:*'
curl 'http://localhost:9200/test/test/_search?q=*:*'

curl -XPUT localhost:9200/test/test/1 -d'{
  "test": "10000"
}'


-- Here is working example without index_name

curl -XDELETE 'http://localhost:9200/test/'
 
curl -XPOST localhost:9200/test/ -d '{
  "mappings" : {
  "test":{
      "properties" : {
        "multi_test" : {"type":"string"}
      }
    }}
  }
}'
 
curl -XPOST localhost:9200/test/test/_mapping -d '{
"test":{
    "properties" : {
      "multi_test" : {
         "type":"multi_field", 
         "fields": {
            "string" : {"type" : "string"},
            "multi_test" : {"type":"float"}
         }
      }
    }
  }
}'
 
 
curl -XPUT localhost:9200/test/test/1 -d'{
  "multi_test": "10000"
}'
 
curl -XPOST 'http://localhost:9200/test/_refresh'
 
curl 'http://localhost:9200/test/test/_search?q=multi_test:*'
curl 'http://localhost:9200/test/test/_search?q=*:*'