Upload multiple attachments may send them in random orders

Using DirectLineJS (not Web Chat) and send the following to the bot.

directLine.postActivity({
  attachments: [{
    contentType: 'image/png',
    contentUrl: 'https://webchat-waterbottle.azurewebsites.net/public/surfacelogo.png'
  }, {
    contentType: 'image/png',
    contentUrl: 'https://webchat-waterbottle.azurewebsites.net/public/xboxlogo.png'
  }],
  text: 'Hello, World!',
  type: 'message'
});

Due to network load speed differ, the bot may receive the two attachments in reversed order.

I looked at network trace, it seems DLJS is the root cause, not the channel.

Start at the DirectLineJS postActivity entry point and reproduce the example with its two image attachments while observing the network trace. Trace the attachment upload and activity-send flow; done means the bot receives attachments in the same order as the input array.