QNetworkAccessManager looses Proxy-Authorization using ssl connection

QNetworkAccessManager looses Proxy-Authorization if https is used in conjunction with an authenticating HTTP Proxy.
I use squid as HTTP Proxy with Digest Authentication. My Access log using https looks like following:

13.09 10:26:21 0 192.168.99.41 TCP_DENIED/407 3620 CONNECT web.de:443 - NONE/- text/html
13.09 10:26:31 10142 192.168.99.41 TCP_MISS/200 52108 CONNECT web.de:443 testuser DIRECT/82.165.229.138 -
13.09 10:26:41 0 192.168.99.41 TCP_DENIED/407 3620 CONNECT web.de:443 - NONE/- text/html
13.09 10:26:51 10124 192.168.99.41 TCP_MISS/200 48895 CONNECT web.de:443 testuser DIRECT/82.165.229.138 -
13.09 10:34:36 0 192.168.99.41 TCP_DENIED/407 3620 CONNECT web.de:443 - NONE/- text/html
13.09 10:34:46 10158 192.168.99.41 TCP_MISS/200 52366 CONNECT web.de:443 testuser DIRECT/82.165.229.138 -
13.09 10:34:56 0 192.168.99.41 TCP_DENIED/407 3620 CONNECT web.de:443 - NONE/- text/html

using http instead of https, my squid access.log looks like this

13.09 10:48:08 0 192.168.99.41 TCP_DENIED/407 3689 GET http://web.de/ - NONE/- text/html
13.09 10:48:08 79 192.168.99.41 TCP_MISS/301 543 GET http://web.de/ testuser DIRECT/82.165.230.17 text/html
13.09 10:48:29 18 192.168.99.41 TCP_MISS/301 543 GET http://web.de/ testuser DIRECT/82.165.230.17 text/html
13.09 10:48:49 17 192.168.99.41 TCP_MISS/301 543 GET http://web.de/ testuser DIRECT/82.165.230.17 text/html

I inspected the network communication with wireshark and found out that after a successful Proxy-Authorization and connection to the destination host all further connections to the same destination using the same proxy need to authenticate again because of missing Proxy-Authorization header.
Using non ssl connection all works fine.
There are 2 Wireshark Dump Files in the example for further investigation.