Unexplained Segmentation Fault with QDialog::show() and QDialog::exec()

[powerofpi]

In a Qt 4.7.1 project in Ubuntu 10.10 x64, I have subclassed QDialog and am calling it in the following way:

//Create a dialog window to get the requested difficulty
    this->generateNewDialog = new GenerateNewDialog(this);
    connect(this->generateNewDialog, SIGNAL(difficultySelected(int)), this, SLOT(generationDifficultySelected(int)));
 
    this->generateNewDialog->exec();

//Create a dialog window to get the requested difficulty
    this->generateNewDialog = new GenerateNewDialog(this);
    connect(this->generateNewDialog, SIGNAL(difficultySelected(int)), this, SLOT(generationDifficultySelected(int)));

    this->generateNewDialog->exec();

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Without fail, this always produces a segmentation fault and crashes my program on the exec() call (not before). Looking at the call stack, the fault occurs at:

QWidgetPrivate::create_sys
QWidget::create
QWidget::setVisible
QDialog::setVisible
show
QDialog::exec

Does anyone see a reason for the behavior? I don't.