Windows: QMainWindow::restoreDockWidget() offsets position of floating dock by window frame

With attached zip file,

1 compile and run
2 clicked the button "Place 0,0" in the main window, observe that floater is move the left top corner.
3 Close application by clicking "X" in main window.
4 Restart application, the position of floater is changed.

To be noted, if the floater is restored by QMainWindow::restoreGeometry(), then it is fine. restoreDockWidget() may not taking title bar size into account.