Observed on various linux flavors (RedHat, OpenSuse), both with Gnome or KDE desktops.

Compile and run the attached example. Make sure the application is maximized.

From the menu do a "Clear saved geometry" to make sure nothing is stored in the settings, then a "Save geometry" followed by a "Restore saved geometry.

Attached images show the results before and after restore: after restoring the geometry the window is maximized, but the widgets inside are restored to the non-maximized geometry only.