When moving an application's main window, any floating QDockWidgets will gradually resize to their minimum size. This is easily reproduced in the dockwidgets example with no alterations. In Qt 6.5+, the example is in qtbase at tests/manual/examples/widgets/mainwindows/dockwidgets. In Qt 6.4.3, the example is in qtbase at examples/widgets/mainwindows/dockwidgets.

Steps To Reproduce:

1. Build the example in Qt Creator against Qt 6.5.3+ (6.6.0 or 6.7.0 snapshot will also work).
2. Run the example.
3. Detach one or more docks so that they are floating.
4. Move the main window around.
   Observe that the floating QDockWidgets size gradually reduces with each movement of the main window.

This did not occur in Qt 6.4.3 or Qt 6.5.2.

If you set a minimum size/width/height for the QDockWidget, it will resize down to that minimum.