node.js上传图片，图片上传不完整，请帮忙解决。

用的代码很简单：

 app.use(express.bodyParser({
uploadDir:__dirname + '/uploadfile/group/icon',
keepExtensions:true,
defer:true,  //enable event
limit:10000000
}));
app.disable("multipart");
app.post('/upload',function(req, res){//bind event handler

req.form.on('progress',function(bytesReceived, bytesExpected){
    console.log(((bytesReceived / bytesExpected)*100)+"% uploaded");});

    req.form.on('end',function(){
        console.log(req.files);
        res.send("done");});
});

但是上传后发现有的图片完整上传，有的不完整，对比如下：

而且奇怪的是bytesReceived竟然比bytesExpected还要大。。