Bot Framework how to end a conversation using node.js with "endofConversation" activity posted?

I am developing using directLine API and bot framework using node.js. Currently, I run into a problem. That is when I use "session.endConversation();" to end a conversation in my bot logic, and then a retrieve the conversation activities using directline apis, there isn't any activities related to endConversation being posted. I was expecting to see some thing like below

{...
  {
    "type": "endOfConversation"
    "id": "CSRTC3lGqTA9jTYpAcsy05|0000006",
    "channelId": "directline",
    "conversation": {
                        "id": "CSRTC3lGqTA9jTYpAcsy05"
                    },
    "code": "completedSuccessfully"
   }
  ...
}

but the activity is not there. It seem the conversation is still on if I kept on posting to the conversation Id. I wonder why is this the case?

via bluecatkaka