@timestamp and logstash-output-mongodb

Hi all,
i have a record sent from filebeat and received by logstash: after some filtering (with grock) the record is sent to mongodb.
The problem is linked to @timestamp field:
"@timestamp" : "\"2016-01-26T14:26:49.333Z\""
As you can see, the " are present...how can i remove them?

How are you populating the @timestamp field?

My conf file doesn't modifiy the @timestamp field: the field is sent "untouched" to mongodb

Does the field come double quoted from Filebeat or are the quotes added somewhere between Logstash's pipeline and MongoDB? Use a stdout { codec => rubydebug } output to inspect what the event look like when it enters the outputs, including mongodb.

Thanks for your reply
i've modified my config file in this way

output {
    mongodb {
      collection => "%{typelog}"
      database => "atest"
      uri => "mongodb://"
      codec => "json"
   stdout { codec => rubydebug }

And this is the stdout output

           "@timestamp" => "2016-01-30T17:12:07.602Z",

I think that this output is correct: this is the same output sent by logstash-output-mongodb plugin to mongodb database?
If so, i have no idea what's wrong...

If the timestamp strings indeed end up as double quoted in MongoDB it does seem like a bug in the mongodb output.