Django将模板呈现为URL

Question

当我向FileUploadForm提交一个空文件时，它无效，我返回以下响应：

return render_to_response('upload.html', {'form': form})

然而，此响应会导致一种奇怪的行为，因为模板内容不会呈现给HTML页面，而是会附加到URL并产生以下请求：

请求网址：127.0.0.1:8000/%3C?xml%20version=%221.0%22%20?%3E%3C!DOCTYPE%20html%20PUBLIC%20%22-//W3C//DTD%20XHTM [ ....]

views.py

def upload_file(request):
    if request.method == 'POST':
        form = SampleUploadForm(request.POST, request.FILES)
        if form.is_valid():
            ...

    else:
        form = SampleUploadForm()

    return render_to_response('upload.html', {'form': form})

upload.html

<form enctype="multipart/form-data" method="POST" action="{% url 'upload_file' %}" id="file_form">
    <input type="button" id="pbutton" value="Select file.." name="pbutton">
    <input type="file" name="file" id="button_file" />
    <div id="label_wrapper">
         <label id="file_label" >No File selected...</label>
     </div>
</form>

已经验证过TEMPLATE_CONTEXT_PROCESSORS，TEMPLATE_LOADERS＆amp; MIDDLEWARE_CLASSES的正确性。