Crash when using 2 QNetworAccessManagers from 2 different threads concurrently

In a GUI application I noticed crashes related to QNetworkAccessManagers running in different threads at the same time.

So I created an "example" console application which contains two different classes (AutoUpdater and PartCheck) which try to receive a page (https://www.twitter.com) from the internet concurrently.
There's a Helper class which starts these two threads.

If you compile and run this application from Creator, you'll notice the following things:

• if both threads are enabled in helper.cpp the result in xterm either the 301 result page of Twitter twice OR none of the threads are finished and xterm says: "Press <RETURN> to close this window..." OR xterm says: "protocol https unknown"
• if you comment out the helper.cpp:11 and 12th line, you'll always see the Twitter redirect page.

In this little example the worst case is that the program ends without SIGSEGV, but in my original GUI application this results in crash.