How to update listview item on download progress?

Question

Given this fairly simple code (based on the GridTemplate)

var list = new WinJS.Binding.List();
    var groupedItems = list.createGrouped(
        function groupKeySelector(item) { return item.operation.group; },
        function groupDataSelector(item) { return item.operation.group; }
    );

    var BackgroundDownloader = Windows.Networking.BackgroundTransfer.BackgroundDownloader;
    var BackgroundTransferStatus = Windows.Networking.BackgroundTransfer.BackgroundTransferStatus;
    
    // TODO: Replace the data with your real data.
    // You can add data from asynchronous sources whenever it becomes available.
    BackgroundDownloader.getCurrentDownloadsAsync().done(function (downloadOperations) {
        downloadOperations.forEach(function (downloadOperation) {
            var download = new Download();
            download.attach(downloadOperation);
            list.push(download);
        });
    });

function Download(operation) {
        var operation;
        var operationPromise;
        var guid;
        var title;
        var progress;

        this.start = function (uri, localFile) {
            this.title = uri.absoluteUri;
            WinJS.Application.local.folder.createFileAsync(localFile, Windows.Storage.CreationCollisionOption.generateUniqueName).done(function (newFile) {
                var downloader = new Windows.Networking.BackgroundTransfer.BackgroundDownloader();
                operation = downloader.createDownload(uri, newFile);
                
                operationPromise = operation.startAsync().then(oncomplete, onerror, onprogress);
            }, error);
        }

        this.attach = function (operation) {
            this.operation = operation;
            this.guid = operation.guid;
            this.title = operation.requestedUri.absoluteUri;
            this.operationPromise = operation.attachAsync().then(oncomplete, onerror, onprogress);
        }

        this.cancel = function () {
            if (operationPromise) {
                operationPromise.cancel();
                operationPromise = null;
            }
        }

        this.pause = function () {
            if (operation) {
                if (operation.progress.status === BackgroundTransferStatus.running) {
                    operation.pause();
                }
            }
        }
        
        function oncomplete () {            
        }

        function onerror(error) {
        }

        function onprogress() {
            progress = operation.progress;
            //todo: update item in listview
        }

    }
    

how do I update the listviews item in the progress handler? I tried list.notifyMutated but it did not do anything and progress.bytesReceived is "undefined".

My template looks like this:

<div class="itemtemplate" data-win-control="WinJS.Binding.Template">
        <div class="item">
            <!--img class="item-image" src="#" data-win-bind="src: backgroundImage; alt: title" /-->
            <div class="item-overlay">
                <h4 class="item-title" data-win-bind="textContent: title"></h4>
                <h6 class="item-subtitle win-type-ellipsis" data-win-bind="textContent: progress.bytesReceived"></h6>
            </div>
            <progress data-win-bind="value: progress.bytesReceived; max: progress.totalBytesToReceive"> </progress>
        </div>
    </div>