Elasticsearch output: timestamp field always set

[cartmanez]

Hi!

Documentation says that timestamp field(with name specified via Time_Key) is only added when Logstash_Format is enabled:

When Logstash_Format is enabled, each record will get a new timestamp field. The Time_Key property defines the name of that field.

However, with the following configuration:

[OUTPUT]
    Name es
    Match *
    Host example.com
    Index my_index
    Type _doc
    HTTP_User user
    HTTP_Passwd ${password}
    Time_Key @another_timestamp

I do get @another_timestamp in every record delivered to elasticsearch even though Logstash_Format is supposed to be off by default.

Can somebody clarify, is it just a documentation issue or not?