Skype Audio call sometimes callerid is the recipientid

I am using Skype Web SDK to implement audio feature. When incoming audio call is detected, I will retrieve the Caller id. Unfortunately, the caller id is sometimes recipient id and sometimes caller id.

    function startAudioCallListener() {
        var conversationsManager = client.conversationsManager;
            conversationsManager.conversations.added(function (conversation) {
                conversation.audioService.accept.enabled.when(true, function () {
                    alert('Incoming Audio call detected from ' + JSON.stringify(conversation.creator.displayName())
                            + "; Caller id()=" + conversation.creator.id());

                });


                conversation.state.changed(function (newValue, reason, oldValue) {
                    console.log('Conversation state changed from', oldValue, 'to', newValue);
                });
            });
        alert("Ready for Incoming Call detection!");
    };

Anyone knows how to get only the caller id when incoming audio call is detected?

Any suggestions are welcome.