Can't resize QMdiSubWindow to a Desktopsize which contains QGLWidget

When resizing QMdiSubwindow to a Desktopsize which contains QGLWidget,
there are some cases that can't resize properly.

One of these cases can be reproduced in the following codes.

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#include <QtOpenGL/QtOpenGL>
#include <QtWidgets/QtWidgets>

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

// create QMainWindow and QMdiArea
QMainWindow* mainWnd = new QMainWindow();
QMdiArea* mdi = new QMdiArea(mainWnd);
mainWnd->setCentralWidget(mdi);
mainWnd->show();
app.setActiveWindow(mainWnd);

// Be sure to confirm that your Desktop size is 1920x1200;
// create one QMdiSubWindow
// This can be resize properly
QMdiSubWindow* subWnd1 = mdi->addSubWindow(new QGLWidget());
subWnd1->resize(1920, 1200);
subWnd1->show();

// create another one
// This can't be resize
QMdiSubWindow* subWnd2 = mdi->addSubWindow(new QGLWidget());
subWnd2->resize(1920, 1200);
subWnd2->show();

return app.exec();
}