This bug occurs under the following conditions: 

Using QNetworkAccessManager

Using QNetworkProxy (HttpProxy) (I have not tested SOCKS)

A POST request to a https:// URL with a QHttpMultiPart and setBodyDevice on a QFile

When you connect the QNetworkReply uploadProgress signal to a slot, the slot will get called a total of 3 times. For example if the file we are uploading is 10MB, on my system the values of the slot in the three calls would be:

16384 / 10000000

10000000 / 10000000

0 / 0

Where those are bytesSent / bytesTotal respectively

Again this only occurs on the condition that you are using a Proxy AND connecting through HTTPs

Proxy + HTTP: Normal working uploadProgress signals

No Proxy + HTTP: Normal working uploadProgress signals

No Proxy + HTTPs: Normal working uploadProgress signals

Proxy + HTTPs: The bug occurs

When viewing my task manager, I notice the file is completely read into memory immediately as I see a 10MB spike in memory when the request starts.  The file transfer does continue on normally until completed.