keyPressEvent does not work in Windows 10 for keyboard modifiers

Steps to reproduce: Windows 10, mingw, QtCreator, all out of the box. 
Take any program and override keyPressEvent. I took addressbook-example, also unmodified except:

void AddressWidget::keyPressEvent(QKeyEvent *event)
{.  
    static int x = 0;
  x++;
}

Put a breakpoint on x++ and start debugging.

Press '1' - breakpoint triggers as expected on PRESSING the key DOWN
Press 'Alt' or 'Ctrl' or any other modifier. Breakpoint triggers when RELEASING the key. This is unexpected.

The same code works on Mac OS as expected, i.e. under Mac OS the breakpoint is always triggered when pressing a key DOWN.

Note: It has nothing to do with the debugger, release code also misbehaves in Windows.