The program has unexpectedly finished

I have an application that was working fine with Creator 3.x.x and Qt 5.4.x. Now I opened and recompiled the project in Qt Creator 4.2.0 and Qt 5.6.2 MinGW. Now I see:

Starting ...\netroute\private\map-generator-build-Qt_5_6_2-Release\release\map-generator.exe...
The program has unexpectedly finished.
...\netroute\private\map-generator-build-Qt_5_6_2-Release\release\map-generator.exe crashed.

If I start debugging, Creator displays an error message saying "During startup program exited with code 0xc0000139".

I don't see even the first qDebug message:

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    qDebug("Starting up"); // ???

I've seen the same issue in another project. However after restarting Creator it's gone. This time even if I restart Creator, I still see the issue.

If I create a deployment directory with all the Qt libraries and platforms/qwindows.dll and copy the app there, it works fine from that directory.

I use a custom MinGW 4.9.3 installed in PATH (see screenshots)