Does setup.template.append_fields work for multifields?

[mbradsher]

Hello,

I am attempting apply the experimental index template feature, setup.template.append_fields, inside a filebeat config in order to set up a multifield datatype. This is an appealing feature because we don't want to have to support the entire field.yml file. I want a multifield datatype that will look like this in the index:

"stepid": {
            "type": "text",
            "fields": {
              "keyword": {
                "type": "keyword",
                "ignore_above": 256
              }
            }
          }

I've attempted to mimic the structure in yaml but I get a different result. I have something like this:

setup.template.overwrite: true
setup.template.append_fields:
- name: fubar.stepid
  type: text
  fields:
    keyword:
      type: keyword
      ignore_above: 256

Unfortunately I get a different result in the index:

"stepid": {
         "type": "text",
         "norms": false
              }

I understand that copying the mapping in the index isn't a foolproof way to develop something but I don't have any other guidance to go on.

What am I missing here?