data.context 在 jQuery File Uploader 的文件上传进度事件上为空

我在使用jQuery文件上传器（blueimp）时遇到问题：

我的实现是完全定制的。我使用图像预览和验证。

我的问题是，即使我在fileuploadadd事件中定义 data.context，当触发fileuploadprogress时，它也是空的。

$('fileinput-element').fileupload({
    url: '/__module/uploadModule/receive',
    type: 'post',
    acceptFileTypes: acceptedFileRegEx,
    dataType: 'json',
    'dropZone': $(dropZone),
    paramName: 'files',
    autoUpload: false,
}).on('fileuploadadd', function (e, data) {
    $.each(data.files, function (index, file) {
        // NOTE: This function call returns a clone of an element that i use as template for upload list items. Works fine.
        var component=uploadModule.getDynamicComponent('listItemContainer');
        // Filling the template (code omitted due to better readabilty)
        // Appending the component to my #uploadList and assigning that to data.context
        data.context = component.appendTo('#uploadList');
    });
    // For manual submittion later on, i fill an array with the data objects from each event call
    dataList.push(data);
}).on('fileuploadprocessalways', function(e,data){
    var index = data.index,
        file = data.files[index],
        node = $(data.context.children()[index]);
    // Further code ommitted due to readability. Here i apply file.preview and (potential) file.error to my list item that is now stored in the variable node. This works fine. My list renders perfectly well.
}).on('fileuploadprogress', function(e, data){
    // PROBLEM: data.context is EMPTY ! Why???
    console.log(data.context);
});

这就是我在单击开始上传按钮时提交所有内容的方式：

$(dataList).each(function(){
    this.submit();
});
// This works well - the uploads are being submitted and sent to the server.

我已经做了广泛的解决方案搜索，测试，试错，调试了1.5天。我只是无法理解这一点。

我做错了什么？

请注意：如果我在 add 事件回调中执行data.submit()，那么当进度事件触发时data.context会正确填充，但我不再可以选择手动启动整个上传队列。