Logstash with metrics plugin does not replace fieldnames like %{my_field}

Hi there,

i want include field values into my metrics record.
Therefore i used add_field and add_tag with my field "%{my_field}".
In stdout and Elasticsearch the content of `add_field` is "New field with value: %{my_field}".
In case of `add_tag` the tag is "metric, %{my_field}".

Here my sample filter:

 filter {
      mutate { add_field => { "my_field" => "hello brave new world" } }
      metrics { 
        add_field => { "foo" => "New field with value: %{my_field}" }
        add_tag => ["metric", "%{my_field}"] 
        meter => ["%{my_field}"] 

What am i doing wrong?

According to the docs this should work:

metrics {
    add_field => { "foo_%{somefield}" => "Hello world, from %{host}" }

I tried logstash versions 1.5.3 and 1.4.4 with the same effect.