Coerce long to double not working

Elastic Stack Elasticsearch
8

I did some more testing, and the actual reason for my problem might be this:
If I send several entries of the same kind with different types at once, the coercion fails (and a mapper_parsing_exception is thrown).
Now look at this example:

ben@ben-ubuntu14:~$curl -XPOST '192.168.56.102:9200/test/persons/' -d '{"name":"Steven", "age":"unknown"}'
{"_index":"test","_type":"persons","_id":"AVGMlpEeWllYL3SlR_qa","_version":1,"_shards":{"total":2,"successful":1,"failed":0},"created":true}
ben@ben-ubuntu14:~$ curl -XPOST '192.168.56.102:9200/test/persons/' -d '{"name":"Martin", "age":25}'
{"_index":"test","_type":"persons","_id":"AVGMltVoWllYL3SlR_qb","_version":1,"_shards":{"total":2,"successful":1,"failed":0},"created":true}

Here, the coercion seems to work.
But funnily, if I GET the entries, see what is returned:

curl -XGET http://192.168.56.102:9200/test/person/AVGMlpEeWllYL3SlR_qa?pretty
{
    "_id": "AVGMlpEeWllYL3SlR_qa", 
    "_index": "test", 
    "_source": {
        "age": "unknown", 
        "name": "Steven"
    }, 
    "_type": "person", 
    "_version": 1, 
    "found": true
}

curl -XGET http://192.168.56.102:9200/test/person/AVGMltVoWllYL3SlR_qb?pretty
{
    "_id": "AVGMltVoWllYL3SlR_qb", 
    "_index": "test", 
    "_source": {
        "age": 25, 
        "name": "Martin"
    }, 
    "_type": "person", 
    "_version": 1, 
    "found": true
}

How can 25 be an integer, when "age" is a string?:

 curl -XGET http://192.168.56.102:9200/test?pretty
"test": {
        "aliases": {}, 
        "mappings": {
            "person": {
                "properties": {
                    "age": {
                        "type": "string"
                    }, 
                    "name": {
                        "type": "string"
                    }
                }
            }
        },