Problem getting some Windows and Dialogs to show.

[billw]

Specifically I have a simply application window that I created using QtDesigner, which worked fine on 4.5.1 but now behaves strangely on 4.7.1: I have to create and then show it twice, it will only show the second time it is created:

QApplication a(argc, argv);
 
	{
		WindowGUIClass w;
 
		w.show();
		w.setFocus();	// <-- this one never appears (even without the enclosing scope causing it to get destroyed)
	}
 
	WindowGUIClass w2;
 
	w2.show();	    // <-- now it will actually appear
	w2.setFocus();
 
	return a.exec();

QApplication a(argc, argv);

	{
		WindowGUIClass w;

		w.show();
		w.setFocus();	// <-- this one never appears (even without the enclosing scope causing it to get destroyed)
	}

	WindowGUIClass w2;

	w2.show();	    // <-- now it will actually appear
	w2.setFocus();

	return a.exec();

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So I hacked my way around that problem after spending a couple of hours trying to work out what the problem is (comparing project settings to a newly created Qt app project, removing ALL extraneous code from the initialization, making it identical to the default generated Qt app).
The only slightly non-standard thing that is in effect when running this program is that it is being spawned by another process rather than started by the user.
Now I have run into another problem: QMessageBox will not display when I use the following code:

inline void show_error(const char* err, const char* title = "Error!")
{
	QMessageBox::critical(NULL, title, err); // <-- nothing appears...
}

inline void show_error(const char* err, const char* title = "Error!")
{
	QMessageBox::critical(NULL, title, err); // <-- nothing appears...
}

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I am using Windows XP 32bit and Qt 4.7.1. My projects were created in 4.5.1, using Visual Studio 2005, and the Qt VS plugin. I am now using VS2008 with the Qt VS plugin.

So, I ask, what is the problem here? Are there any commonly known problems with getting windows to show? I have tried stepping though the code that is supposed to show the window, but to no avail...

/edit So I managed to fix the QMessageBox not displaying by giving a parent QWidget rather than NULL. I also noticed that when the parent IS NULL, the setVisible(true) call buried in the critical() function generates a Windows error sound... Qt bug?!