Beats eats my timestamp with pre-formatted JSON

stdout.json

2016/01/06 23:15:27.708044 publish.go:100: DBG  Publish: {
  "@timestamp": "2016-01-06T23:15:23.210Z",
  "beat": {
    "hostname": "ip-172-31-46-141",
    "name": "ip-172-31-46-141"
  },
  "count": 1,
  "fields": null,
  "input_type": "log",
  "message": "{ \"@timestamp\": \"2016-01-06T23:15:20+00:00\", \"@version\": \"1\", \"vhost\": \"untergeek.com\", \"clientip\": \"80.240.139.191\", \"bytes\": 60375, \"duration\": 0.114, \"status\": 200, \"request\": \"/feed/\", \"method\": \"GET\", \"referrer\": \"-\", \"useragent\": \"Fever/1.39 (Feed Parser; http://feedafever.com; Allow like Gecko)\"  }",
  "offset": 8765843,
  "source": "/var/log/nginx/untergeek.com.access.log",
  "type": "nginx_json"
}