When having a QTabWidget where each tab contains a QMdiArea, moving QSubWindows from one mdi area to another i.e. from one tab to another tab, then the subwindows state does not seem to be preserved correctly.

If the subwindow is moved from a tab that is hidden, then that subwindow cannot gain focus and the z-ordering of the subwindows is incorrect. The window without focus is always on top.
On Mac there are also painting issues when removing a subwindow from a visible tab.