Dynamic template: eager_global_ordinals not applied

Elastic Stack Elasticsearch
1

Hello,

After inserting a dynamic template for a new field in all indices using:

PUT myindices-*/_mapping/mytype
{
  "dynamic_templates": [
    {
      "MyField_field": {
        "mapping": {
          "fielddata": {
            "loading": "eager_global_ordinals"
          },
          "index": "not_analyzed",
          "omit_norms": true,
          "type": "string"
        },
        "match_mapping_type": "string",
        "match": "MyField",
        "_all": {
          "enabled": false
        }
      }
    }
  ]
}

and after inserting some data for this new field (no data existed for this field before inserting the dynamic template), I checked mappings on a random index, and this is what I got:

"mytype" : {
        "_all" : {
          "enabled" : true,
          "omit_norms" : true
        },
    "dynamic_templates" : [ {
    [...]
    {
      "MyField_field" : {
        "_all" : {
          "enabled" : false
        },
        "mapping" : {
          "fielddata" : {
            "loading" : "eager_global_ordinals"
          },
          "index" : "not_analyzed",
          "omit_norms" : true,
          "type" : "string"
        },
        "match" : "MyField",
        "match_mapping_type" : "string"
      }
    },
    [...]
    "properties" : {
    [...]
      "MyField" : {
         "type" : "string",
        "index" : "not_analyzed",
        "fielddata" : {
        "format" : "disabled"
        }
      }
   [...]

Why is the "format" set to "disabled" in the mapping and not to "eager_global_ordinals" as expected by the dynamic template?

I'm using ES 2.2.1.

Thanks for your help,
MG