Knockout notification valueToNotify behavior

Knockout notification callbacks receive valueToNotify if callbackTarget not supplied, but don't receive it when there is a callbackTarget.

HTML

<script src="https://github.com/downloads/SteveSanderson/knockout/jquery.tmpl.js"></script>
<script src="https://github.com/SteveSanderson/knockout/raw/master/build/output/knockout-latest.debug.js"></script>
<div id="console">
    <h2>Log</h2>
    <div id="log"></div>
</div>

CSS

#console {
    margin-top: 2em;
    padding: 0.2em;
    background: #eeeeff;
}
#console button {
    float: right;
}
#log {
    clear: both;
    font: 8pt monospace;
}

JavaScript

var observable = ko.observable('initial value');
var target = new Object();

observable.subscribe(function(notifiedValue) {
    log("notify without target received " + notifiedValue);
});
observable.subscribe(function(notifiedValue) {
    log("notify with target received " + notifiedValue);
}, target);

observable('new value');



///////////////////////

function log(message) {
  $("#log").append(document.createTextNode(message)).append("<br/>");
}

function clearLog() {
    $("#log").empty();
}