Calling hide() and show() on QDialog may result in X errors

Calling hide() and show() in sequence on a QDialog may result in the following X errors:

X Error: BadWindow (invalid Window parameter) 3
Major opcode: 20 (X_GetProperty)
Resource id: 0x16095c7
X Error: BadWindow (invalid Window parameter) 3
Major opcode: 15 (X_QueryTree)
Resource id: 0x16095c7
X Error: BadWindow (invalid Window parameter) 3
Major opcode: 40 (X_TranslateCoords)
Resource id: 0x16095c7

This happens with 4.3 and 4.4

The following example reproduces the problem:

#include <QtGui>

class Dialog : public QDialog {
    Q_OBJECT

public:
    Dialog(QWidget *parent = 0) : QDialog(parent) {
        QPushButton *b = new QPushButton("hide/show", this);
        connect(b, SIGNAL(clicked()), this, SLOT(foo()));
    }

public slots:
    void foo() {
        hide();
        show();
    }
};

#include "main.moc"

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

    Dialog dialog;
    dialog.show();

    return app.exec();
}