Is URLConnection.SendingProgressed.BytesLeft TotalBytes instead?

The headline says almost all.
I am using URLConnection’s event to monitor server connection progress and speed.
This works very ok for ReceiveProgress which will always fire at least at 100% progress for small files.
This does not work by the book – at least on macOS – where SendingProgress for small uploads always fires at exactly 50% only – giving me the same sizes for BytesSent and BytesLeft.
So I wonder: Is BytesLeft TotalBytes in reality?

Edit:

http://documentation.xojo.com/api/networking/urlconnection.html#urlconnection-sendingProgressed

You may want to add the sum of both for the total progress

If it only fires at a part, that’t a bug