Cached QDialog does not redraw when closing dialog using 'X' button

We moved project from 5.7.x to 5.12.4 and face the issue with QDialog.

When QDialog is closed and we execute QDialog::exec second time the QEvent::Paint is not called. When you close Dialog using Escape key or with custom button it works properly.

When you resize window or call QWidget::repaint the QEvent::Paint is called but in more complicated views it bombards you with asserts.

I have found workaround to override close event (which also prevent asserts):

    void closeEvent(QCloseEvent* bar) override
      {
      bar->ignore();
      hide();
      }

In attachment you can find test project.