If these lines are the other way round, the buttons don't appear on MacOSX!
@ -139,8 +139,8 @@ class InstallWizard(WindowModalDialog, MessageBoxMixin):
button.setChecked(True)
vbox.addStretch(1)
self.set_layout(vbox)
vbox.addLayout(Buttons(CancelButton(self), OkButton(self, _('Next'))))
self.show()
self.raise_()